Flocking is a skydiving discipline in which a small group of wingsuiters (generally under 12) will fly together in a pre-arranged formation (which would be prepared for and rehearsed on the ground).
Participants exit the plane separately at 12,000-15,000ft and dive their suits to catch the rabbit (the person who acts as the base of the formation and sets the speed/pace). Once together, the group may have arranged to perform vertical or horizontal manoeuvres to change the shape of the group.
As with all Wingsuit skydiving, the flock will fly a pattern designed to lead the group to a location close to their landing area at the point that the parachutes need to be opened (around 3000ft). This pattern will usually be a U-shape [click image bottom left], designed to lead the group parallel to, but not over, the flightline (the path along which other groups and skydivers are dispatched from the plane). Inthe image bottom left the white line is the line along which freefallers are dropped, the blue arrow is the point at which the wingsuiter exits, the red line is the flight pattern and teh dark red line is the parachute path.
The group will break-off at around 5,000ft in order to give each flyer sufficient space to open their parachute without risking collision with another jumper. This is because parachute and freefall collisions can lead to serious injury or fatality.