A meet, $\wedge$ is an operation defined on elements of a poset $P$ (not necessarily all of them) defined as:

The join (or Greatest lower bound) of $a, b \in P$ is an element $a \wedge b \in p$ such that:

(a) $a \wedge b$ is a lower bound of $a$ and $b$: thus $a \wedge b$ \preceq a and $a \vee b \preceq b$;

(b) $a \wedge b$ is the greatest such lower bound: i.e., if there exists $c \in P$ such that $c \preceq a$ and $c \preceq b$ then $c \preceq a \vee b$.

Note that, if it exists, a join is necessarily unique.

See also Lattice (algebraic structure)