An organised look at the risks and hazards in the premises. It should point out the hazards and the risks associated with the hazards. It should identify where people are at risk, and it should prioritise the measures deemed necessary to eliminate or minimise the risk. It should also point out what is already in place protecting relevant persons.
A risk matrix is effective esepcially when used to create an action plan stating hi/medium/low priority etc.
I have seen some great ones, done in a simple systematic format by hand, and some terrible ones all wrapped up in fancy folders, on facny paper, "qualified" assessor etc. (You know the type, 30 pages of standard text followed by a tick box that would about pass as a daily checklist)