Real Function/Secant/As line/Definition

Secant

For a function

$f\colon T\longrightarrow \mathbb {R}$

defined on a subset ${}T\subseteq \mathbb {R}$ and two distinct points ${}a,b\in T$, the line through ${}(a,f(a))$ and ${}(b,f(b))$ is called the secant of ${}f$ at ${}a$ and ${}b$.