Often times, the duty to support a spouse does not terminate with the end of a marriage. In cases in which one spouse is not self supporting or the parties' income are so different that a court would declare them "unconscionable", alimony (also known as ‘spousal support’) becomes a factor. Whether alimony is appropriate and, if so how much should be paid is decided on a case by case basis.
In our modern world, the most common form of alimony is "rehabilitative". This is alimony for a period of time to allow the one spouse to get back into the work force or improve his or her career opportunities. This type of alimony typically terminates after a specified period of time. There is also ‘indefinite” alimony which is what is sounds like – alimony that lasts for an indefinite period of time. This type of alimony goes on until circumstances warrant that it end.
Both types of alimony can either be modifiable or non-modifiable. In other words, the court (or the parties by agreement) may say that Husband shall pay Wife a specified amount, but he or she may come in at any time and ask for a modification if circumstances change.
By contrast, sometimes the court or the parties by agreement will say the number cannot change. It is important to note that once a party “waives” alimony, he or she can never come back and request it.