"Spousal support" is really, legally, just another name for "alimony." But there may be a tendency to use this term for longer term or permanent support versus shorter, temporary support.
We've already addressed the basics of spousal support under "Alimony" toward the top of this page; but, here we can add that the duration of spousal support for marriages that lasted less than 10 years is generally half the length of time that the marriage lasted. And, for marriages that lasted over 10 years, it is not uncommon for spousal support to continue for life, until the supported spouse remarries, or until the court sees fit to take new action.
A spouse on "permanent" support might, for example, be taken off spousal support if he/she suddenly gets a high-paying job or major new source of income.