A fursuit is a costume - typically an anthropormorphized animal costume - worn by a furry. Hiqh-quality fursuits are really fucking expensive, as in thousands of dollars. Just like a rapper wearing a 5-pound gold chain, this does not give the furry himself any additional value.

Fuck, those costumes are expensive, $1049 for [a typical fursuit] and $1119 for [a fancier fursuit] and that's the discount price. I imagine furries then spend even more to get them altered so that they have an opening in the groin area so that they can have sex while wearing them. -- Bantustan 02:50, 1 February 2010 (UTC) in The TJC

People who wear fursuits are known as furries.
It is important to note that while not all fans of the Furry subculture own or wear fursuits, the only reasons any of them don't is because they're on welfare. All of them at least have ears and a tail, if not a full suit, or at least want one.
The primary reason furries wear these costumes is because deep in what remains of their souls they know full well what they are doing is sick and wrong. Despite the endless blather that they are just having some fun, or are connecting with their animal totem or Fido enjoys having his asshole stretched they are deeply ashamed of who they are but do not have the balls to off themselves.
That is not an exaggeration - furries never allow people to take a photograph of them without the headpiece on because they are (in almost every way) fucking pussies.
The second reason some furries wear these suits is because they believe their pet will be more willing to fuck if they too look like animals. This is not very likely however because because any dog that still has the will to live will recognize them for what they are - heartless, brainless, dickless freaks - and tear them inside