I basically means that he/she reached orgasm, usually during sexual activity. The 'climax' referring to the height of the orgasm as it's obviously releasing and satisfying. Or in cruder terms, he/she came. Don't feel silly or anything though for asking the question. There are lots of words these days for different things so don't feel stupid just because you don't know them all!
Also, just ignore your friends. So what if you don't know all the terms? In my eyes it's a good thing you only knew the meaning for it in literature terms! Just shows you must be a sensible teenager.
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If one day you wake up and find that you're missing me,
And your heart starts to wonder where on this earth I can be,
Thinking maybe you'd come back here to the place that we'd meet...