Determinism of all sorts has a common meaning: The past state of a system determines its future state. Historical determinism is essentially this idea applied to history, forming a sort of teleology. The present and future are determined entirely by the past. You'll note that there isn't much room here for people to influence the future by actions in the present, something academics call agency. Modern determinists will rarely say there's no room for agency in determining the future. Instead they often retreat into probabilistic arguments and say that "on average" agency follows deterministic laws.

Historical determinism is a very broad term however. It can include everything from political teleologies (e.g. tribes --> chiefdoms --> states) to economic strategies (e.g. feudalism --> capitalism --> socialism) to "racial characteristics" and other ridiculous ideas. Within historical determinism is a subset that considers geographic environment as in some way constraining and shaping societal changes. In small doses this is a fairly uncontroversial idea. After all, you couldn't (reasonably) build a rice paddy if you're living in the middle of the sahara. But in larger degrees it runs into issues, which I've detailed some of in a previous post