Let be a category, a set, and $(X_i){i \in I}\mathscr{A}$. A product of $(X_i){i \in I}P$ and a family of maps \(\Bigl(P \stackrel{p_i}{\longrightarrow} X_i\Bigr)_{i \in I}\) with the property that for all objects $A$ and families of maps \(\Bigl(A \stackrel{f_i}{\longrightarrow} X_i\Bigr)_{i \in I}\) there exists a unique map $\bar{f}{\colon}\linebreak[0] A \to Pp_i \circ \bar{f} = f_ii \in I$.