An object $𝑐$ in a category $\mathrm{𝒞︀}$ is terminal if there is a unique morphism from any other object into it.

Because terminal objects are unique up to unique isomorphism (as are all universal objects) we often just write $\top$ to refer to the terminal object. Likewise, $!:𝑑\to \top$ refers to the unique morphism into $\top$.