The word Negro was used in the English-speaking world to refer to a person of black ancestry or appearance, whether of African descent or not, prior to the shift in the lexicon of American and worldwide classification of race and ethnicity in the late 1960s. The word "negro" means "black" in Spanish and Portuguese, from the Latin niger ("black"). The usage was accepted as normal, even by people classified as Negros, until the Civil Rights movement.
During the American Civil Rights movement of the 1950s and 1960s, some African American leaders in the United States objected to the word, preferring Black, because they associated the word Negro with the long history of slavery, segregation, and discrimination that treated African Americans as second class citizens, or worse. During the 1960s Negro came to be considered an ethnic slur.
The term is now considered archaic and offensive, and is not commonly used. It is still used in some historical contexts, such as in the name of the United Negro College Fund. and the Negro league in sports.
The United States Census Bureau announced that Negro would be included on the 2010 United States Census, alongside "Black" and "African-American," because some older Americans still self-identify with the term.
Around 1442 the Portuguese first arrived in sub-Saharan Africa while trying to find a sea route to India. The term negro, literally meaning "black", was used by the Spanish and Portuguese as a simple description to refer to people. From the 18th century to the late 1960s, "negro" (later capitalized) was considered the proper English term for all people of sub-Saharan African origin.
It fell out of favor by the early 1970s in the United States after the Civil Rights movement. However, older African Americans from the period when "Negro" was considered acceptable, initially found the term "Black" more offensive than "Negro". Evidence for the acceptability of "Negro" is in historical African-American organizations and institutions' use of the term—such as the United Negro College Fund. In current English language usage, "Negro" is generally considered acceptable in a historical context, such as baseball's Negro Leagues of the early and mid-20th century, or in the name of older organizations, as in Negro spirituals, the United Negro College Fund or the Journal of Negro Education. The U.S. Census now uses the grouping "Black or African American." In 2010 the U.S. Census added the term "negro" in efforts to include older African Americans. This revival of the term is controversial. 
A specifically female form of the word—negress (sometimes capitalized) —was sometimes used; but, like "Jewess", it has all but completely fallen from use. (An exception is its extremely unusual use in the titles of paintings, drawings and sculptures, largely as an allusion to the formerly common occurrence of the word in such titles, but such usage has dropped off dramatically.) Both are considered racist and sexist although, as with other racial, ethnic, and sexual words that are seen as pejorative, some people have tried reclaiming the word, for example artist Kara Walker. 
The related word Negroid was used by 19th and 20th century racial anthropologists. The suffix -oid means "similar to". "Negroid" as a noun was used to designate a wider or more generalized category than "Negro"; as an adjective it qualified a noun as in, for example, "negroid features".
In Portuguese, negro is an adjective meaning the color black, as in 'black' person. However, preto is the most common antonym of branco (white), while negro can be condescending, since it is a word generally associated with higher registers. In Brazil the word is not considered disrespectful, and is the appropriate manner to refer to black people, though it is often considered impolite to take note of an individual's skin color in any context (which causes the word to be used only in reported speech or in third-person). In Brazil and Portugal negro is the most respectful way to address the African ethnicity, with preto being considered a racial slur.
In Spain, negro (note that ethnonyms, names of nationalities, etc. are generally not capitalized in Romance languages) means "black person" in colloquial situations, but it can be considered derogatory in other situations (as in English, "black" is often used to mean irregular or undesirable, as in "black market/mercado negro"). However, in Spanish-speaking countries such as Argentina, Chile, and Uruguay where there are few people of African origin and appearance, negro (negra for females) is commonly used to refer to partners, close friends or people in general independent of skin color.
It is similar to the use of the word "nigga" in urban communities in the U.S. For example, one may say to a friend, "Negro ¿Como andas? (Literally, "Hey, black one, how are you doing?") In this case the diminutive negrito is used, as a term of endearment meaning "pal", or "buddy" or "friend." Negrito has come to be used to refer to a person of any ethnicity or color, and also can have a sentimental or romantic connotation similar to "sweetheart," or "dear" in English. (In the Philippines, Negrito was used for a local dark-skinned short person, living in the Negros islands among other places)
In other Spanish-speaking South American countries, the word negro can also be employed in a roughly equivalent form, though it is not usually considered to be as widespread as in Argentina or Uruguay (except perhaps in a limited regional and/or social context).
In Haitian Creole the word nèg, derived from the French "nègre", refers to a dark-skinned man; it can also be used for any man, regardless of skin color, roughly like "guy" or "dude" in American English.
The Dutch "neger" is generally (but not universally) considered as neutral, or at least less negative than "zwarte" (black one).
In German, Neger used to be considered a neutral term for black people, but gradually fell out of favour from the 1970s. Nowadays it is usually considered a racist slur due to its phonetic similarity to nigger, and only used without racist connotation by members of the pre-baby boomer generation. Otherwise, the term Schwarzer (black person) is preferred or Farbiger (colored person). There is a candy traditionally called Negerkuss (literally "negro kiss"), but the name has come to be used less.
In Russia the term "негр" (negr) was commonly used in the Soviet period without any negative connotation, and its use continues in this neutral sense. In modern Russian media, the word is used somewhat less frequently - "африканцы" ("Africans") or "афро-американцы"("Afro-Americans") are used instead, depending on the situation), but is still common in oral speech. The word "black" (чёрный) as a noun used as a form of address is pejorative, although it is primarily used with respect to peoples of the Caucasus, natives of Central Asia, and not black people. The word "black" (чёрный) as an adjective is also used in a neutral sense and means the same as "негр" (negr), e.g. "чёрные американцы" (black Americans), "чёрное население" (the black population), etc. Other alternatives to "негр" are темнокожий (temnokozhiy - "dark-skinned"), чернокожий (chernokozhiy - "black-skinned"). These two are used as both nouns and adjectives.
In Italy negro was used as a neutral term until the end of the 60's. Nowadays the word is considered offensive in some contexts; if used with a clear offensive intention it may be punished by law. Neutral words to define a black or dark-skinned person are nero (arcaism of negro, literally "black") or di colore (coloured - or literally 'of colour').
In Swedish neger used to be considered a neutral term for black people, but the term has gradually fell out of favour through the 1960s, 1970s and 1980s. Today the neutral term to define a black person is svart ("black"). There is a Swedish pastry traditionally called negerboll (literally "negro ball"). Due to its possible offensive character, the name has fallen out of favor in for example new cooking books, though it is still used colloquially.
In Finnish it is unclear whether the word neekeri (negro) was considered a neutral term for black people. Very few — if literally any — black people lived in Finland before the 1960s. The term has gradually fallen out of favour ever since, and has been replaced with the neutral musta ("black"). In 2002 neekeri's definition was changed from perceived as derogatory by some to generally derogatory in line with ryssä (Ruskie) and hurri (Swede) in Kielitoimiston sanakirja. Also, there was a popular Finnish pastry called Neekerinsuukko (lit. "negro's kiss"). The manufacturer changed the name to Suukko ("kiss") in 2001. Today, neutral terms to define a black person include musta ("black"), tumma (lit. "dark-shaded"), tummaihoinen ("dark-skinned") and mustaihoinen ("black-skinned").