Certain posets $X$ have a binary operation meet denoted by $\land$, such that $x\land y$ is the greatest lower bound of $x$ and $y$. Such posets are called meet-semilattices, or $\land$-semilattices, or lower semilattices.

If $m$ and $m^{{\prime}}$ are both meets of $x$ and $y$, then $m\leq m^{{\prime}}$ and $m\geq m^{{\prime}}$, and so $m=m^{{\prime}}$; thus a meet, if it exists, is unique. The meet is also known as the and operator.