A latch (called sneck in Northern England) is a type of mechanical fastener that is used to join two (or more) objects or surfaces together while allowing for the regular or eventual separation of the objects or surfaces.
Note that a latch is not the same as the locking mechanism of a door or window, although often they are found together in the same product.
A latch typically engages another piece of hardware on the other mounting surface. Depending upon the type and design of the latch, this engaged bit of hardware may be known as a keeper or strike.
Latches range in complexity from flexible one piece flat springs of metal or plastic, such as are used to keep blow molded plastic power tool cases closed, to multi-point cammed latches used to keep large doors closed.
Latch bolt: This is an extremely common latch type. Typically part of a lockset, it is a spring-loaded bolt with an angled edge. When the door is pushed closed, the angled edge of the latch bolt allows it to retract. Once the door is fully closed, the spring engages and the latch bolt fully extends and holds the door closed. The latch bolt is disengaged (retracted) typically when the user turns the door handle, which via the lockset's mechanism, manually retracts the latch bolt, allowing the door to open.
Deadlatch (entry) includes an extra tongue to prevent shimming.