Ooh my prescription is somewhat similar to yours (can't remember exactly but I'm around -2.5) which is long sighted and when I take my glasses off after wearing them for long periods I can hardly make out anything. I don't think it's that bad as lens prescriptions can go way past -3.0 and they also go into + for short sighted people. I was told the thicker your lenses the worse your eyesight is but then again I wouldn't know much I only wear glasses and don't study optometry
The bigger the number (either negative or positive), the worse the defect; negative numbers mean you are short-sighted and positive ones mean you're long-sighted. -2.5 is bad enough to need glasses for driving and probably for most other distance work, but usually not totally incapacitating, as in you wouldn't be walking into doors without your glasses. I am also -2.5 and -2.75 and wear glasses all the time, but can manage without if I have to, as long as I don't have to drive or do any distance work (looking at a projector or TV).
mild-moderate short sightedness. see helenia's comments.
p.s. lenses are measured in dioptres. a plus (convex) lens of +1 dioptre causes parallel light rays to be focussed to a point 1 metre away. A +2 dioptres causes parallel light rays to focus at 1/2 a metre. +3D at 1/3 metre etc. Minus (concave) lenses make light rays diverge by an equivalent amount.