The standard math symbol for infinity is the sideways figure‑eight: ∞.

In mathematical writing, you’ll usually see it written as ∞\infty ∞, and in LaTeX it’s typed with \infty. This symbol is called the lemniscate and it’s used to represent an unbounded or limitless quantity, such as in limits like x→∞x\to \infty x→∞ or intervals like (−∞,∞)(-\infty,\infty)(−∞,∞).