Featuring, often abbreviated to ft or f/ is a term used in the music industry to credit a musician who is not the main artist for their performance on a song or, on occasion, an album. The number of songs with a featured artist has increased considerably in the 2000s, although artists being featured can be traced back to the start of singles charts, with the first use of the term in the UK Singles Chart in July 1954 by "The Four Aces featuring Al Alberts" with "Three Coins In The Fountain" at 5th place. 
Featured artists are most common in rap and dance music, with rap albums usually containing a large number of different artists on various different songs. Dance producers frequently use different vocalists on each of their songs, often crediting them as featured. Featured artists are typically more common on artist's singles than album tracks, although many albums also included featured artists on non-single tracks also.
Usually the artists who feature on songs perform a small part, such as a verse of the song, or on occasion simply play an instrument. On occasion, however, the featured artist performs the chorus. This is most common in rap music, where the main artist (the rapper) will perform the rap verses, with a vocalist performing the actual singing on the track. Mainstream examples of this include "Go Hard" by DJ Khaled featuring Kanye West and T-Pain and "Heard Em Say" by Kanye West featuring Adam Levine of Maroon 5.
The act of being featured on a single occasionally causes controversy or confusion, in that for some artists being "featured" is considered derogatory. There are also often strange cases of an artist being featured, often when they don't contribute to the track significantly at all. One example of this is Mario Winans' 2004 release "I Don't Wanna Know", which featured Enya, even though she didn't perform on the track at all. Enya's being featured was in fact attributed to the song using a sample from her 1987 instrumental "Boadicea" (The Celts). Occasionally, a featured artist might actually get more time singing or rapping than the main artist. This is prominent in Timbaland's Give It to Me, in which featured performers Nelly Furtado and Justin Timberlake sing more part of the song than Timbaland himself.
When singles are released in multiple territories, the artist credit is often changed to reflect the artist's popularity in that area. For example, the 2006 single "I Belong to You" was credited to "Anastacia ft. Eros Ramazzotti" in the United States of America, but to "Anastacia and Eros Ramazzotti" in Central Europe, to reflect Ramazzotti's popularity in the Central European area.
Featured artists are also on occasion referred to by other terms, seemingly used to increase their importance. Common examples are "Fly On The Wings Of Love", by XTM and DJ Chucky Presents Annia, and "In Private" by Pet Shop Boys with Elton John.