A place of a commutative unital ring has different meanings in the literature:
The most common one is an equivalence class of (archimedean or non-archimedean) absolute values. (An absolute value is a non-trivial multiplicative seminorm.) This convention is often used in number theory, where it applies to number or function fields.
Other notions of places can be imagined, combining the three above classical examples.
The notion of place in number theory is interesting because it is at the heart of the geometric study of zeta functions. An improvement on this notion is given by the setting of global analytic geometry, which includes trivial seminorms that allow a natural geometric definition of adele?s and idele?s.