Square LEDs are available in both through-hole (THT) and surface mount (SMD) packages. Their lens shape is square.
For SMD LEDs, a square lens usually means a square package. Square or rectangular packages are ideal for placing multiple LEDS side-by-side without gaps. This offers a uniform light output and is idea for LED displays.
Square through-hole LEDs have a square or rectangular shaped package on leads. The square package is ideal for panels which require a square shaped indicator and again allow for flush mounting.