Services over http and services over tcp

I was looking at my organizations service architecture. I was told by some one that we have two types of services. "One over HTTP" and "other over TCP". Moreover, services over TCP have no WSDL's.

I have two very basic questions:

a) What is the difference between services over HTTP and services over TCP? Do Soap and rest web services come under both the categories?

b) If we don't have web services definition language, how can we know what are the operations a service exposes ?