Depends on how you are using the term mitre???
A mitre is something thats cut at an angle, for instance you could use a mitre block to cut wood to join two pieces of wood together so they fit together perfectly, so for instance if someone said "you will need to mitre the coving so it fits together with the other piece then you would cut the piece of coving at a 45 degree angle and the other piece at 45 degree angle to fit together.
a mitre is a type of woodworking joint, a cut usually at 45 degrees, in two pieces of wood so they form a 90 degree square where they meet. think picture frames - where they joint at the corner is a good example of where a mitre joint would be used. also kitchen worktops are often jointed with a kind of mitre.
usually done with a mitre box and saw or better still a chop saw.