There are several types of lock step in waltz dancing, including International Standard waltz. A "lock step" is when the moving foot approaches to the standing foot and crosses in front of or behind it, creating a "check" position.
There are several locking steps in waltz, including: the back lock, which is a Bronze syllabus figure; the turning lock, of the Silver syllabus; and the turning lock to right, of the Gold syllabus.
The back lock is a Bronze syllabus step. It is a progressive figure borrowed from quickstep. It is commonly used as the ending to a progressive chassé to right.
The forward lock is the same figure as the back lock, only with reversed roles between leader and follower.
The turning lock is a Silver syllabus step. It transitions from a right turning figure into a left-turning one.
The turning lock to right is a Gold syllabus step. It was only added to the ISTD syllabus after 1966, due to its increasing popularity.