Equal angle (EA) is an L-shaped steel section with both legs the same length. Common Australian sizes are 25x25x3, 40x40x5, 50x50x5, 75x75x6, and 100x100x10 mm. The non-equal version is unequal angle (UA), where one leg is longer than the other.
Angle iron is the universal bracket and ledger material. Cut a length, drill or weld it to a wall or post, and you have a horizontal shelf or ledger. It's also the standard 'jamb' for receiving the latch face of a steel gate, with the latch tongue catching the angle's vertical leg.
Not usually a primary structural section in gate frames (RHS or SHS does that better) but a constant supporting role.