What it actually means
An SLA is the part of a business connectivity contract that sets out, in plain numbers, what the provider has signed up to deliver. The usual ingredients are an uptime percentage, often quoted as 99.5%, 99.9%, or 99.99%, a response time for when you log a fault, a target repair time, and a schedule of service credits that pay back into your account if those targets are missed. The higher the uptime figure, the less downtime you are accepting per year. 99.9% allows roughly 8 hours and 45 minutes a year. 99.99% allows around 52 minutes.
The trap is that an uptime number on its own tells you almost nothing about how a bad day will actually feel. Two providers can both quote 99.9% and behave completely differently when the line drops at ten on a Monday morning. The detail that matters sits in the repair window, the support response, the escalation path, and whether anyone is actually answering the phone.
At home
What this looks like in the house
Worth saying for context: home broadband almost never carries a meaningful SLA. The consumer code from Ofcom gives you some protection on missed appointments and delayed repairs, but you are not buying a guaranteed uptime figure on a domestic line. That is one of the real differences when a business moves from a consumer style product onto a proper business connection.
In business
What this looks like at work
The felt cost is the hold music your customer is listening to while your phones are dead. It is the queue forming at the till because the card terminal cannot reach the bank. It is the prospect filling in your competitor's form because your inbound number rang out for twenty minutes. An SLA does not stop those moments by itself, it sets out what is supposed to happen next and what compensation is owed if your provider does not deliver. The trick when you read one is to look past the uptime headline and ask what the repair commitment is, who picks up at three in the morning, and how clearly the credits actually arrive on your bill without you having to chase.