A single swing gate is exactly what it sounds like: one leaf, one set of hinges. Compared to a double swing, the single is simpler (one latch, one set of hinges, no meeting stile to seal) and faster to install.
The practical limit is around 3.5 m wide. Beyond that, the leverage on the hinges is so high that maintaining plumb gets difficult. A 4 m single swing leaf weighing 80 kg generates 1.6 kN-m of moment at the bottom hinge. Three hinges, oversized stile, and post depth at least 800 mm in 400 mm dia. concrete are the typical responses.
Most residential pedestrian gates are single swings. Single-leaf driveway gates show up where the opening is under 3 m and the property doesn't justify a sliding-gate installation.