1. Refers to the obligation of one person to contribute, in part or in whole (sometimes called a payor), to the cost of living of another person. Maintenance is usually expressed in a currency amount per month as in "$450 a month maintenance."
Some countries prefer the words "support" (spousal or child support) or "alimony" but they all mean the same thing.
2. Maintenance is also the term of an archaic crime and tort in reference to the encouragement given to another to sue a third-party.
From Russell on Crimes, 1826:
"An unlawful taking in hand or upholding of quarrels or sides, to the disturbance or hindrance of common rights.... intermeddles in a suit depending in a court of justice".
It differs from champerty as the latter implies that the intermeddler has a stake in the litigation interfered with.
In McIntyre Estate v. Ontario (2002), 218 D.L.R. (4th) 193 at canlii.org/en/on/onca/doc/2002/2002canlii45046/2002canlii45046.html, the Ontario Court of Appeal defined maintenance in relation to the included tort of champerty:
"Maintenance is directed against those who, for an improper motive, often described as wanton or officious intermeddling, become involved with disputes (litigation) of others in which the maintainer has no interest whatsoever and where the assistance he or she renders to one or the other parties is without justification or excuse.
"Champerty is an egregious form of maintenance in which there is the added element that the maintainer shares in the profits of the litigation.
"Importantly, without maintenance there can be no champerty.
"The courts have made clear that a person’s motive is a proper consideration and, indeed, determinative of the question whether conduct or an arrangement constitutes maintenance or champerty. It is only when a person has an improper motive which motive may include, but is not limited to, officious intermeddling or stirring up strife, that a person will be found to be a maintainer.