Definition
A written commitment about service performance (response time, resolution time, uptime, coverage hours) usually with a stated consequence if the terms are missed. Common in B2B and managed-service contracts, an SLA replaces vague words like 'fast' or 'reliable' with numbers both sides have agreed to in advance.
What it looks like in practice
Two SLAs sit on a commercial cleaning owner's desk. The one he signed with a property manager says nightly crews arrive within the agreed window, a missed area gets re-cleaned by the next business day, and any complaint gets a reply within four business hours, with a service credit if it does not. The other is the one he holds his supply distributor to: next-day delivery on chemicals, with a stated remedy when it slips. When a building manager complained twice in one month, the written terms turned a shouting match into a short conversation about which clause had actually been missed.
Why it matters
An SLA cuts both ways for an owner. Signing one with a client is a promise that can carry penalties, so the terms have to match what the business can hit on its worst week, not its best. Buying a service, the SLA is the leverage. It is what lets you point at a clause instead of arguing about whether a vendor has been slow. The usual mistake is over-promising: committing to a response time nobody staffs for turns a trust-building document into a monthly source of credits and friction. Read the exclusions on both sides; that is where the real coverage is decided.