Is an advisory the same as a fault?

Not quite. Since 2018, MOT results use defect categories: Dangerous and Major defects fail the test outright. Minor defects don't fail the test, but they are still an actual, existing defect - just not serious enough to fail the car.

An advisory is different again. It doesn't fail the test, and rather than flagging something that's already defective, it's the tester noting that a component looks like it'll need attention before too long - for example tyres wearing towards the legal limit, or early signs of corrosion. It's a heads-up, not a current fault.

For a buyer, advisories are genuinely useful reading: they're the tester's best guess at what you'll likely need to spend money on next, even though the car has a clean pass today.

Source: gov.uk: how the new MOT defect categories work