A two rider bicycle with the riders side-by-side.

The side by side seating is in contrast to a tandem where the riders sit one behind the other. These are also commonly built with more than two wheels. In theory one could be built with three or more riders but I have not been able to find evidence of one outside of large multi-rider, multi-wheel vehicles like the various "party bikes" where typically most of the riders face across the direction of travel.