\begin{definition}[Definition:Initial Topology/Definition 2]
Let $X$ be a set.
Let $I$ be an indexing set.
Let $\family {\struct {Y_i, \tau_i} }_{i \mathop \in I}$ be an indexed family of topological spaces indexed by $I$.
Let $\family {f_i: X \to Y_i}_{i \mathop \in I}$ be an indexed family of mappings indexed by $I$.
Let $\tau$ be the coarsest topology on $X$ such that each $f_i: X \to Y_i$ is $\tuple {\tau, \tau_i}$-continuous.
Then $\tau$ is known as the '''initial topology on $X$ with respect to $\family {f_i}_{i \mathop \in I}$'''.
\end{definition}