A 'bare-metal server' is a computer server that is a 'single-tenant physical server'.The term is used nowadays to distinguish it from modern forms of virtualization and cloud hosting.
Bare-metal servers have a single 'tenant'. They are not shared between users. Each server may run any amount of work for the customer or may have multiple simultaneous users, but they are dedicated entirely to the customer who is renting them. Unlike many servers in a data center, they are not being shared between multiple customers.
Bare-metal servers are 'physical' servers. Each logical server offered for a rental is a distinct physical piece of hardware that is a functional server on its own. They are not virtual servers running in multiple on shared hardware.