A path from node n1 to node n2 with regards to a variable v is def-clear, only if v is not given a new value at any of the nodes in the path and the use in n2 is a c-use.

A du-path (or: DU path) is a def-clear path from a node n1 where a variable v is defined to a node n2 where v is used.

100% all-defs coverage with regards to variable v requires that for all definitions of v all corresponding uses have been covered.

A def-use pair (or: DU pair) is a pair of nodes (n1, n2) where a variable v is defined at n1 and used at n2 and all paths from n1 to n2 are def-clear.