Turnover
A turnover is a single round or square of pastry folded in half over its filling, sealing it into a portable half-moon or triangle.
It is the simplest sealed pastry: one piece of dough, one fold, one crimped edge. Puff pastry turnovers puff open at the seam if underfilled or oversealed, so leave a clean border and vent the top.
The line between a turnover, a hand pie, and a pasty is mostly regional vocabulary and pastry choice.