Cushioning is staying in touch with other romantic prospects while in a relationship, to soften the blow if it ends.
Cushioning is keeping one or more backup options on the side while you are already seeing someone. The cushions are there to soften the landing if the main relationship falls apart.
The behavior usually looks harmless from the outside. Flirty messages with an ex, keeping a dating app installed, or maintaining a too friendly chat with someone who clearly likes you.
Most cushioning happens when a person feels unsure about their relationship but is not ready to leave or to fully commit. The cushions are insurance against being alone.
It is a form of emotional, and sometimes physical, infidelity. Even when nothing overt happens, the energy and attention are being diverted away from the partner.
Cushioning often points to deeper doubts. If you find yourself lining up backups, the more honest move is usually to address what feels shaky in the relationship rather than to keep a safety net warm.
It is related to benching and breadcrumbing, which describe how the cushions themselves are often kept on hold.