At my school it means scrutinising planning and books, observations of teaching and progress data.
At first it was all 3, every half term, but in an attempt to cut down on workload and stress (class teachers and SMT doing the monitoring) it has now changed to data scrutiny and pupil progress meetings taking priority, with short snapshot observations.
If it is then felt there is an issue with progress from these, then books are scrutinised more thoroughly, there may be more 'drop-ins', and there is feedback and support. If that doesn't raise standards and increase progress then planning is scrutinised in depth, with more feedback and support.
So basically if your progress data is good, you're not monitored much as the assumption is that things must be going ok. This is a good thing generally, although there is then the issue of data being fudged, but this is normally ok as moderation keeps things in check.