Complex sentence: Pending changes is a review system that prevents certain edits from being publicly visible until they're approved by another editor; the system temporarily deployed on the English Wikipedia was a modified form of the system in use on a number of other Wikimedia projects.
Split into simpler sentences: Pending changes is a review system that prevents certain edits from being publicly visible until they are approved by another editor. The system temporarily used on the English Wikipedia was a modified form of the system in use on a number of other Wikimedia projects.