In reply to Greenbanks:
> Daughter Greenbanks' school has asked for a "visa and OV7" for her forthcoming trip to NY. Got the visa - but what is an OV7?
If that's really what they said, they haven't a clue.
If you ring the US Embassy (at £1/minute) they'll say "a visa? What kind of visa?". Needs to be a specific type, probably B2 in this case, and you probably don't need one since she'll qualify under the Visa Waiver Programme.