A high performance version of the Honda Civic (Si stands for 'Sport Injected'). While the Civic Si(SiR in Canada) was traditionally a Hatch, the latest body style (FA5 Sedan & FG2 Coupe) more closely resemble the standard Civic. Designed to be more powerful than a base Civic, but not as much as a Type R, these are popular for their affordability and performance, as well as the large availability of parts available.
Some like the new Honda Civic Si Coupe and Sedan, but I prefer the Hatchback EP3 body style.
by EP3-Hatch May 21, 2009
1. A make believe sports car designed to appeal to those who are too poor and broke ass to afford a European car, who are jerk-off's, and hope to make friends with other waterheads who think their Honda Civic Si's are cool.(Also Si owners are sometimes liberal cowards, but they mostly drive Subaru Foresters)

2. An insult, usually aimed at anyone who falls in the above category, but there can be special exceptions.
1. My Honda Civic Si is so cool lolz, I think I'm going to go park near a handicap spot and pick up some babes!

2. Wow! That fat kid with the man tits in my gym class runs as fast a Honda Civic Si.
by Your Mom Likes Dong September 18, 2008