magnetic dip

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

• noun The angle that a magnetic needle makes with the horizontal plane at any specific location. Magnetic dip is 0° at the magnetic equator and 90° at each of the magnetic poles.

from the GNU version of the Collaborative International Dictionary of English.

• noun The angle that a magnetic needle makes with the plane of the horizon.

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

• noun The angle between magnetic north and the horizontal (as shown by a compass held vertically).

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

• noun (physics) the angle that a magnetic needle makes with the plane of the horizon