The Collaborative International Dictionary
Lock step \Lock" step`\n.
A mode of marching by a body of men going one after another as closely as possible, in which the leg of each moves at the same time with the corresponding leg of the person before him.
Hence: (fig.) The slavish copying of one person's actions by another; as, party members who vote in lockstep with the leadership.
Wikipedia
Lock Step refers to any of several dance steps that involves the "locking" of the moving foot: the moving foot approaches to the standing foot, crosses in front of or behind it in the direction of the approach, stops close to the standing foot, and the weight is fully transferred to the (previously) moving foot.
The closeness of the feet so that the lower legs of the dancer are "locked" together crossed is the main difference from other cross-steps used, e.g., in the Grapevine, where the moving (crossing) foot travels away from the standing foot and the lower legs are separated. In the Whisk the crossing foot travels around the standing foot, rather than "locks" from the direction of approach.
The term "lock step" or simply "lock" may be applied either to a single "locking" step or to a whole step pattern, e.g., of three steps, such as "step diagonally forward, lock behind, step diagonally forward". The footwork varies depending on the actual dance figure.
Lock steps are popular in Quickstep.
Usage examples of "lock step".
Staff Sergeant Duncan followed him in lock step and stood at attention.
Through the whispers rapped the boot heels, Beverly Dyson's and those of the three men in lock step a pace behind him.
Through the whispers rapped the boot heels, Beverly Dysons and those of the three men in lock step a pace behind him.
Then Render was moving, a combination of blows, high, low, and high again, forcing the younger man to move back in lock step with him.
They moved one lock step forward, crowding to make a wall he couldn't breach.