I've heard the British term "half seven" (or "half nine," "half five", etc) used to tell time. I can't remember though if it means 6:30 or 7:30 (i.e. half *an hour before* seven, or half *past* seven)?

I'm American and have never heard another American use the phrase, but apparently it's very common in the UK.
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*Half seven* is the same as *half past seven*, with *past* simply missing. It's **7:30**.
Americans say "half *past* seven". I've never heard anyone say "half *before* seven" nor have I heard an American say "*half seven*". It does lead to odd situations. My German wife has a very good English friend. She learned the difference between "half seven" and "*halbsieben*" when they both showed up on time yet an hour apart.