It means that in a sealed water resistance test thing, the watch, sitting there surrounded by water, will still function when subjected to, in the case of your

It means that in a sealed water resistance test thing, the watch, sitting there surrounded by water, will still function when subjected to, in the case of your watch, 3bar of pressure. That is without moving the watch, with the crown fully tightened/pushed in, etc. Yours was probably defective, or was advertised in bad faith, even though by those water resistance tables they say 30m isn't suitable for swimming. However, I've taken both 3 bar and 5 bar watches to the sea many times with no problem. It's supposed to handle shallow swimming