alternation

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

• noun Successive change from one thing or state to another and back again.

from The Century Dictionary.

• noun The act of alternating, or the state of being alternate; the reciprocal succession of things in time or place, or of states or actions; the act of following something and being in turn followed by it: as, the alternation of day and night, cold and heat, summer and winter.
• noun Passage back and forth; repeated transition; the action of going from one state, condition, or point to another, and back again, indefinitely: as, alternation between states of mind or between places; his alternations from one point to the other were very frequent.
• noun In mathematics: The different changes or alterations of order in numbers. More commonly called permutation.
• noun Alternate proportion (which see, under alternate, a.).
• noun 4. In church ritual, the saying or reading of parts of a service by minister and congregation alternately.
• noun In phytogeography, the discontinuous occurrence of a plant type due to local variations in the conditions. See the extract.
• noun In electricity, the time of one reversal, or one half-wave of alternating current. One alternation therefore is one half-cycle. The frequency of an alternating current formerly was given in alternations per minute. See alternating.

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

• noun The reciprocal succession of things in time or place; the act of following and being followed by turns; alternate succession, performance, or occurrence.
• noun (Math.) Permutation.
• noun The response of the congregation speaking alternately with the minister.
• noun See under Generation.

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

• noun The reciprocal succession of (normally two) things in time or place; the act of following and being followed by turns; alternate succession, performance, or occurrence; as, the alternation of day and night, cold and heat, summer and winter, hope and fear.
• noun The response of the congregation speaking alternately with the minister.
• noun linguistics ablaut
• noun logic The "inclusive or" truth function.
• noun mathematics A sequence that alternates between positive and negative values. (Sometimes wrongly used to mean a permutation.)

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

• noun successive change from one thing or state to another and back again