Many dances (both Smooth and Latin) use one form or another of the lock step element (Quickstep, Foxtrot, Waltz, Tango, Cha Cha, West Coast Swing, etc.). Quickstep is the first dance that you think of when you think of lock steps (forward and backward locks) and W.C. Swing is probably the last one you think of (example: lady's right foot locking behind in the Sugar Push).
The lock step is composed of three actions:
The step before the lock step (prep step) must cross the track (be taken in CBMP*) of the leg that is to lock. The crossing step (taken on rise)is lead through the rotation of the hips rather than from rotating the whole upper frame.
The lock step is danced on rise and the legs lock (cross) just below the knees. The movement of the lock step is powered from the crossing leg (prep step). The trailing leg is pulled into the crossed leg with an immediate weight change to the locking leg. The trailing leg controls the closing speed of the lock (example: a lock step in Foxtrot would close much slower than a lock step in Quickstep or Cha Cha). When dancing a back lock, there is a slight heel drag as the locking foot moves to the rise position (this will keep the body from leaning backwards through the shoulders).
The unlock is executed on the same foot as the prep-step. When the weight is moved from the locking foot to the next step (unlocking step) the hips rotate as the foot lowers from rise so the next step does not lock.
A typical Quickstep forward lock step is danced: Quick, Quick, Slow (left, right, left). The first Quick is the prep-step, the second Quick is the forward lock, and the Slow is where the unlocking happens as you lower from rise. However, in Cha Cha locks (three locks in succession) the normal unlock step is used to both "unlock and prep" for the next lock step. So the hips rotate from unlocking to the crossing prep-step on the same step. On a forward lock you would prep with the right leg, lock with the left leg, then the right leg would unlock and immediately prep to lock again with the right leg, etc.
* CBMP - Contra Body Movement Position is a foot position achieved by placing the moving foot slightly across and in front of or behind the supporting foot. It usually does not contain CBM (Contra Body Movement). This is the turning of the body against the supporting foot in the direction of the moving leg (a body position).