Confusingly, this dual concept is called a source from $Y$ in $C$, even though the term ‘source’ has another meaning, one which we just used in the definition! One can of course say ‘domain’ instead of ‘source’ for this other meaning, but that leads to other confusions. Or one can say ‘cosink’ for a source in the sense dual to a sink, since a source from $Y$ in $C$ is the same as a sink to $Y$ in the opposite category$C^{\mathrm{op}}$.

Structured sinks

If $U\colon C\to D$ is a functor, then a $U$-structured sink is a collection of objects $X_i\in C$ together with a sink in $D$ of the form $\{U(X_i) \to Y\}$. This notion figures in the definition of a final lift.

Examples

Any cocone under a diagram is a sink; indeed a cocone is precisely a sink indexed by the objects of the domain of the diagram together with a commutativity condition for the arrows in the diagram.