Oh god what is a cocktail dress and where to find one?

[ElephantsAndMiasmas]

I need to get one for a dinner event coming up, apparently. Shops all full of nice summery dresses but are cocktail dresses different in some way?

Am panicking because only have this weekend to go shopping. So advice on 1) what the feck constitutes a cocktail dress exactly? and 2) any nice ones in existence at the moment would be amazing!

www.clothingattesco.com/dresses/f+f-sweetheart-neckline-dress
Rubbish at links and don't suppose this will work but google it. Comes inink & black and is only £16!!!

Or even 'pink' and black!

ooh which one, mcfee?

This is described as a bridal dress but I would consider wearing it as a cocktail dress and it comes in under budget.
What do you think?

www.monsoon.co.uk/bridal-dresses/carmel-bridal-dress/invt/85343792/&bklist=icat,5,shop,women,dresses,bridesmaiddresses#