A lowercase Greek letter commonly used to denote inclusion maps, embeddings, or indexing variables in mathematics.
Examples
Inclusion mapping notation
\iota: A \hookrightarrow B
Complex unit vector component
\vec{v} = v_1\hat{i} + v_2\hat{j} + v_3\hat{k} + v_4\hat{\iota}
Index variable in summation
\sum_{\iota=1}^n x_{\iota}