Does someone know what this notation means? It is in the context of one period of a trigonometric function (when a function approaches infinity)

2. $x \to \frac{\pi}{2}^-$ means "make $x$ approach $\frac{\pi}{2}$ from the left".

$x \to \frac{\pi}{2}^+$ means "make $x$ approach $\frac{\pi}{2}$ from the right".

3. and "from the left" means that $x<\frac \pi2$.
"from the right" is the other way round