Friends are the people who ask if you're okay when it's obvious that you're not. Friends are the people who offer to help, even when they know they probably can't. Friendship isn't always about doing something for the other, it's the willingness to do it if asked or even offering to do it before asked. Acquaintances are everybody else.
By being someone who always tries to do the right thing, I have a bad habit of failing to differentiate the two.