Crimping is pressing or folding the edge of pastry dough together to seal in a filling, usually leaving a decorative wavy or ridged edge.
It can be done with fingers, the tines of a fork, or a fluted pastry wheel, and is used on pie crusts, empanadas, calzones, and Cornish pasties. Thinner doughs generally need a gentler touch, while thicker doughs can take a more pronounced crimp.
Crimping is distinct from fluting, which refers specifically to a scalloped decorative edge rather than the functional seal that keeps filling from leaking out during baking.