miter joint

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A joint made by beveling each of two surfaces to be joined, usually at a 45° angle, to form a corner, usually a 90° angle.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A joint between two members at an angle to each other; each member is cut at an angle equal to half the angle of the junction and usually joint at right angles to each other.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun joint that forms a corner; usually both sides are bevelled at a 45-degree angle to form a 90-degree corner