Not sure what the exact definition of a velomobile is, but I think it's mostly about being fully enclosed in an aerodynamic shell, so it can be 2 wheeled as well which are faster than the 3 wheeled type (being more narrow and lower rolling resistance). Without the shell, a three wheeled recumbent is just referred to as a trike.
There are some amusing encounters on YouTube between velomobiles and police who are generally confused by these things, thinking they are motorized when, in fact, they are not. They are simply fast because they minimize drag. Other than that they fall into the same broad class of human powered vehicles that conventional bikes are part of