A timetable clash is when you have two teaching events scheduled at the same time.
Students are expected to attend all scheduled teaching events in their course of study. This means that you are expected to attend all of your lectures, tutorials, laboratories, etc. for all of your papers.
However timetable clashes may be permitted in certain limited circumstances, in which case they are assessed under two categories:
You are not normally permitted to have more than one timetable clash per week per teaching period.