1. collapsing or compressing inward in a series of folds, like the bellows of a concertina
Usage: present participle of concertina; commonly used in British English
2. moving or progressing in a jerky, accordion-like manner with alternating expansion and contraction
Usage: figurative use

Examples

• The car's front end was concertinaing after the collision.
• The train cars were concertinaing together in the crash.
• The fabric concertinaing effect created an interesting visual pattern.
• The metal accordion was concertinaing as the musician played.
• The pile of boxes concertinaing under the weight made storage difficult.
• The caterpillar moved by concertinaing its body segments forward.