[temp.constr.constr.general]

A constraint is a sequence of logical operations and operands that specifies requirements on template arguments.

The operands of a logical operation are constraints.

There are five different kinds of constraints:

(1.1)
conjunctions ([temp.constr.op]),
(1.2)
disjunctions ([temp.constr.op]),
(1.3)
atomic constraints ([temp.constr.atomic]),
(1.4)
concept-dependent constraints ([temp.constr.concept]), and
(1.5)
fold expanded constraints ([temp.constr.fold]).

In order for a constrained template to be instantiated ([temp.spec]), its associated constraints shall be satisfied as described in the following subclauses.

[Note 1:

Forming the name of a specialization of a class template, a variable template, or an alias template ([temp.names]) requires the satisfaction of its constraints.

Overload resolution requires the satisfaction of constraints on functions and function templates.

— end note]