Final answer:
A Combination lock is the type that historically used letters for its combinations. They offer portability and an array of possible combinations using a sequence of characters that act as a key.
Step-by-step explanation:
The type of lock that often used letters rather than numbers for combinations is a Combination lock. These locks, which have been popular for their portability and ease of use, typically feature a dial or rings with a sequence of letters or numbers that must be aligned to unlock. Users select a sequence of characters to set as their combination, and this unique sequence acts as the key to open the lock.
Combination locks are commonly found in settings like schools and gyms, where they are used to secure lockers. Historically, some combination locks used letters for their combinations to provide a greater range of possible combinations, as opposed to the more modern practice of using numerical combinations. This feature made them quite distinctive among portable locking devices.