A hot desk is a term used to describe a recruitment environment that is already established for a recruiter.
This usually means that there is already a system in place and a database of candidates and clients for the recruitment consultant to work with. See more on a recruitment consultant here.
In this case, the recruiter does not need to be as concerned with the basics of setting up a recruitment business and rather can focus on building and expanding the recruitment network at hand.
The alternative to a hot desk is a cold desk, which is an environment where there is no recruitment network in place for a recruiter to work with. See more on a cold desk here.