Definition of "bunching"

The foreign ladies, in their simple, tasteful, fresh attire, innocent of the humpings and bunchings, the monstrosities and deformities of ultra-fashionable bad taste, beamed with cheerfulness, friendliness, and kindliness.

1974, Isabella Bird, Six Months in the Sandwich Islands, amongst the Palm Groves, Coral Reefs and Volcanoes

Why do we sometimes find three buses on the same route arriving together at a bus stop? What is the explanation of bunching? […] Meanwhile there are other buses following on the same route. The 600-yard interval between the second and third bus is decreased by every second's delay to the leaders, and before long the third bus has caught up. That is why buses sometimes arrive at the bus stop in bunches.

1949 July and August, Railway Magazine, page vii, advertisement by London Transport