Lockable means able to be locked or secured with a lock. A lockable door has a keyhole or latch that lets you lock it shut. A lockable bike chain can be fastened with a padlock to keep your bicycle safe. A lockable storage box protects your valuables by letting you secure the lid with a combination lock or key.

The word describes anything designed with a locking mechanism. Your parents might keep important documents in a lockable filing cabinet at home. Schools use lockable lockers so students can safely store their belongings during the day. A lockable gate keeps unwanted visitors out of a yard or building.

Something being lockable doesn't mean it's currently locked, just that it can be locked when needed. A lockable toolbox sitting open on a workbench isn't locked right now, but it has the capability to be secured when the owner wants to protect the tools inside. The opposite would be something like a simple cardboard box, which has no way to lock it no matter how much you might want to.