A
marriage license (or
marriage licence) is a document that grants governmental
permission to get married according to the
laws of the place where the license was issued. Requirements vary a lot from place to place; typical requirements for a marriage license include:
The license is usually
valid only for a certain period of time; if the participants don't have whatever constitutes a legal ceremony of marriage within 30 or 90 days (or whatever the limit is) the license to marry is no longer valid. However, some
jurisdictions also require a
waiting period, so that one has to wait, say, at least 24 hours, between applying for the license and receiving it, or receiving it and getting married. (Locations without
residency requirements or waiting periods often get visits from people who want to marry immediately and cannot in their home area.)
Most governments charge some kind of fee to issue a marriage license. From the viewpoint of those getting married, this all may just seem like extra paperwork, but marriage license records are very useful for genealogists and historians researching past marriages and families.
Sources:
http://www.weddingdetails.com/questions/license.cfm
http://www.1800bride2b.com/articles/marriagelaws_chart.htm
http://marriage.about.com/library/bllic.htm