Hosts that use the cPanel control panel will often advertise the ability to host additional domains as "addon domains". It's a common feature to be able to host multiple domains on a shared hosting account. Many, if not most such accounts, come allow an "unlimited" number of domains to be hosted. Obviously, "unlimited" is more of a marketing word, it's not really infinite. At some point the number of domains in itself could become an issue for the server, and the "resources abuse" clause will come into effect.
Anyway, if you want to be extra safe, contact the host about the particular package that you're interested in, and they should be able to clarify the situation for you.