calendar month

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

• noun The period of duration from the same date of one month to the same date of the next month, and thus can be 28, 29 during a leap year, 30 or 31 days long. For example the duration from 21st January to 20th February.

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

• noun one of the twelve divisions of the calendar year