The word waif (from the Old French guaif, stray beast) refers to a living creature removed, by hardship, loss or other helpless circumstance, from his or her original surroundings. The most common usage is to designate a homeless, forsaken or orphaned child, or someone whose appearance is evocative of same.
As such, the term is similar to a ragamuffin or street urchin, although the main distinction is volitional: a runaway youth might live on the streets, but would not properly be called a waif as the departure from one's home was an exercise of free will. Likewise, a person fleeing their home for purposes of safety (as in response to political oppression or natural disaster), is typically considered not a waif but a refugee.
Orphaned children, left to fend for themselves, are common as literary protagonists, especially in children's and fantasy literature. The characters Heathcliff in Emily Brontë's 1847 novel Wuthering Heights and Pip in Charles Dickens' 1861 novel Great Expectations are waifs. Dickens, it may be noted, has been called "the Master of Waif Literature." Bret Harte's 1890 novel A Waif of the Plains, set against the backdrop of the Oregon Trail in the 1850s, is another example. The children in A Series of Unfortunate Events are usually waifs, in between their unsuccessful stints in the care of various relatives.
Literary waifs are frequently depicted with a frail appearance, although such physical aspects are not inherent in the term. Such evocations may reflect the endemic malnutrition of the street urchin.
Chicago's Mercy Home for Boys and Girls, a long-term residential home for troubled young men and women from the streets and abusive homes, has published The Waif's Messenger for more than 100 years.
In nautical terms, a waif is any survivor of a shipwreck compelled to make land upon a foreign shore. In this sense it is roughly synonymous with castaway, although the latter term is generally associated with isolation; a waif (in the nautical sense) usually indicates a survivor of a marine disaster who has fallen into the care and/or custody of others.
"Some seven years ago...there appeared the remarkable saga of Manjiro, the shipwrecked Japanese waif who was rescued and brought to the United States by a Yankee whaling captain." 
The noun waif has a secondary nautical meaning, referring to any message that has been received via flag signals.  However, in that context the etymology is most likely divergent, springing instead from the Old Norse veif, a back-and-forth movement.
Many other songs use the word "waif" to romanticize street children and runaways, as in the Marc Almond song "Waifs and Strays", or the Steely Dan song "Janie Runaway", which describes the title character as being the "wonderwaif of Gramercy Park".
In botany, a "waif" is an unusual species found in the wild that is alien and either a) is unsuccessful at reproduction without human intervention, or b) only persists a few generations and disappears. Such a plant never gets "naturalized" in the wild. "Waif flora" also refers to plant species which occur on oceanic islands due to chance long-distance dispersion of seeds.
"The waif look" was used in the 1960s to describe thin, large-eyed models such as Twiggy and Dorothee Bis. The "gamine" look of the 1950s, associated with actresses like Audrey Hepburn (who starved as a teenager during the Dutch famine of 1944), Leslie Caron and Jean Seberg, was, to some extent, a precursor.
The term "waif" was seemingly ubiquitous in the 1990s, with heroin chic fashion and models like Kate Moss and Jaime King on the runways and in advertisements. Actresses like Ally McBeal star Calista Flockhart, Winona Ryder, recently the British actress Keira Knightley and singer Celine Dion have all been pinned with the term.
Although the heroin chic look has gone out of fashion, it still holds some popularity in Hollywood. For example, Wonderbra model Eva Herzigova was criticized over her waif-like figure. Daily Mirror columnist Sue Carroll wrote:
The supermodel, looking like a throwback to the 'heroin chic' era of waif-like undernourished models, was an X-ray of her old self, skeletally thin with greasy hair, blue lips, a cold sore and sunken eyes.—