Squire = El-cheapo Japanese made Fender
Standard = Usually Mexican; a definate step up, but play before you buy because the quality will varry a good bit.
American Standard = Made in the US, top quality.

But that's all a very rough idea. A lot of the reissues are made in Japan and they usually play and sound pretty good. Then there's a line of American guitars with thinner finishes which are electronically structurally the same, but are cheaper due to the lower cost finish.