What is a vise?

A vise is a kind of tool that is used to hold something together or still between two "jaws" of a sort; you might think of it as being like a mouth, and the teeth bite together to hold something in place, like if you were holding a pen in your teeth.
Vises can also be used to hold together, for example, two things that have been glued together so that they dry in place and stick as well as possible. The two "jaws" are usually brought closer together through some kind of screw or a lever. You will often see a vise mounted on the edge of a workbench or table, as that is where they are often most useful and will fit right in with other metal tools.