Semantics
Semantics of a(n) X gives the meaning, or an interpretation of the meaning, of X. Where X could be a word, sign, sentence, program etc. Common use: Let's not argue about semantics. Of course when some one says that you know that now is the time to argue about semantics. After all, if that individual is implementing a policy using words, but doesn't want to talk about the meaning of those words, you know that person plans to twist the meaning after the policy takes effect. Essentially the policy will no longer resemble the discussion that precluded the decision to accept that policy.
That's the danger, but in reality semantics should always be clear for words. In programs, semantics are generally accepted to be the results of running the program on any input.