A slot is a connection dedicated to one user on a server. For example, a 4 slots server will be able to welcome up to 4 users at the same time.
In computers, a slot, or expansion slot , is an engineered technique for adding capability to a computer in the form of connection pinholes (typically, in the range of 16 to 64 closely-spaced holes) and a place to fit an expansion card containing the circuitry that provides some specialized capability, such as video ...