This is also an acronym for Service Level Agreement. This is an agreement between the provider of a service and the customer which defines the service in measurable terms. Most often the service is defined in the amount of time that it is available. Commonly referred to as "five nines" (for 99.999%, or "seven nines" for 99.99999%, which requires a maximum of 3 seconds of downtime a year. There was a story about this at slashdot.org at http://slashdot.org/article.pl?sid=01/08/27/1419238&mode=nested

SLAs have also been defined by the number of users who can connect at a time, performance benchmarks, dial up availability, and usage statistics. The agreement can be either a custom creation between the parties involved, or a pre-defined standard agreement.