A punctuation symbol representing horizontal ellipsis to indicate continuation of a sequence or omitted terms.
Examples
Sequence notation
x_1, x_2, x_3, \ldots, x_n
Infinite series
1 + \frac{1}{2} + \frac{1}{4} + \frac{1}{8} + \ldots
Matrix elements
\begin{pmatrix} a_{11} & a_{12} & \ldots & a_{1n} \\ a_{21} & a_{22} & \ldots & a_{2n} \\ \vdots & \vdots & \ddots & \vdots \\ a_{m1} & a_{m2} & \ldots & a_{mn} \end{pmatrix}