When they say a car is "stock" what do they mean. i know it has to do with importance but what exacly does it mean?

sorry im tired i ment to say performance*, not importance

Stock means straight from the factory with no modifications.

what makes it so speacail?

It's not special. It's completely plain; exactly the same as every other car from the factory.

one example of where stock would be preferable is when you own a rare car. most MR2 owners, for instance, would not modify a 1995 Turbo, as there were fewer than 300 imported to the US in it's final year here. Also, classic cars are generally worth more stock, or restored to stock condition, than if they are modified...

Stock: Honda S2000
Modified: Vortech Supercharged S2000

:)