A chicken suit is a novelty costume

Costume

The term costume can refer to wardrobe and dress in general, or to the distinctive style of dress of a particular people, class, or period. Costume may also refer to the artistic arrangement of accessories in a picture, statue, poem, or play, appropriate to the time, place, or other circumstances...

 that exaggerates the features of chicken

Chicken

The chicken is a domesticated fowl, a subspecies of the Red Junglefowl. As one of the most common and widespread domestic animals, and with a population of more than 24 billion in 2003, there are more chickens in the world than any other species of bird...

s. Chicken suits usually fit someone up to 6' 1" and 200 lbs.
A chicken suit can be used at parties

Party

A party is a gathering of people who have been invited by a host for the purposes of socializing, conversation, or recreation. A party will typically feature food and beverages, and often music and dancing as well....

 and other events or as a costume for school mascots

Mascot

The term mascot – defined as a term for any person, animal, or object thought to bring luck – colloquially includes anything used to represent a group with a common public identity, such as a school, professional sports team, society, military unit, or brand name...

. Some chicken barbecue companies bring a chicken suit with them for members of the group for whom the barbecue is held to wear in order to advertise the event.

Once, as a joke

Joke

A joke is a phrase or a paragraph with a humorous twist. It can be in many different forms, such as a question or short story. To achieve this end, jokes may employ irony, sarcasm, word play and other devices...

, European ice skater Oksana Baiul

Oksana Baiul

Oksana Serhiyivna Baiul is a Ukrainian professional figure skater. She is the 1994 Olympic Champion in Ladies' Singles and 1993 World Champion.-Early and personal life:...

 entered the ice skating rink wearing a chicken suit.

For an episode of the MTV

MTV

MTV, formerly an initialism of Music Television, is an American network based in New York City that launched on August 1, 1981. The original purpose of the channel was to play music videos guided by on-air hosts known as VJs....

 show Jackass

Jackass (TV series)

jackass is an American reality series, originally shown on MTV from 2000 to 2002, featuring people performing various dangerous, crude, ridiculous, self-injuring stunts and pranks...

, skateboarder Tony Hawk

Tony Hawk

Anthony Frank "Tony" Hawk , nicknamed "The Birdman" is an American retired professional skateboarder and actor. Hawk gained significant fame for completing the first 900 as well as his licensed video game titles distributed by Activision...

 drove through a looping ramp in a chicken suit.