Suggest merging FGproperties/Systems/static into this article and changing the name
The pitot system measures impact pressure and is basically a tube pointing forward.
Small aircraft have one, small IFR aircraft have one or two (of which at least one is heated) and larger commercial aircraft have three or even more. In those large aircraft the left pitot serves the pilot instruments, the right the co-pilot and the third system the back-up instruments. This might be different for each type of aircraft of course.