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.
[2] The back lock is a Bronze syllabus step.
[3] The turning lock is a Silver syllabus step.
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.