Crimping
Crimping is sealing and decorating the edge of a pie by pressing the pastry layers together in a repeating pattern, with fingers or a fork.
The seal matters more than the decoration: a well-crimped edge keeps the filling in and gives the rim its structure. Egg wash between the layers before crimping makes the seal stronger.
Finger crimping gives the classic scalloped wave; a fork gives straight ridges and is faster for hand pies.