Civility is the name of a policy on Wikipedia, is part of Wikipedia's Five Pillars, and the values it expresses are admirable and clear: for Wikipedia to be a successful collaborative project, all participants must be respectful and considerate of others, even when—especially when—there are disagreements. Don't attack others, and don't waste people's time.
It's basically Wikipedia's equivalent of the Golden Rule.
However, like "Wikipedia is not a battleground", the fact is Wikipedia's community will tolerate a substantial amount of incivility, especially when the incivil editor is also known for making good contributions to the encyclopedia otherwise.
Indeed, Wikipedia editing can inflame passions, and maintaining civility can be a challenge. All the usual advice follows: take a deep breath, walk away from the computer, and try again when you calm down. The better you get along with others, the more successful you'll be.