A turn-lock is a bag closure mechanism consisting of a tab or paddle that rotates a quarter-turn to lock into a receiving plate. The Chanel CC turn-lock — the interlocking double-C logo that opens and closes the Classic Flap — is the most famous example. The mechanism is elegant, quick to operate, and provides a satisfying physical click when engaged.
Turn-locks were common across luxury bags in the mid-twentieth century. Hermès uses a turn-lock on the Kelly (called a 'cadenas' closure). Celine's Classic Box has its own turn-lock version. The mechanism adds formality — it signals a bag that takes a moment to open, which is appropriate for the most refined pieces.