small pinhole side of my iPad what is it for

NOT everyone!

Everyone that comes here looking for help, don't always know the things that you know.

When trying to post to help someone here, never assume the person/user that posts here their level of tech/Apple product knowledge. Ever.

If you are talking about the little hole at the top of an iPad right above the camera and the hole on the back of the iPad near the top hole, they are microphones. If your talking about the hole on the right hand side of the iPad, you can stick a SIM ejector tool in carefully and eject a tray where you can insert a SIM card to make your iPad usable with cellular data and send and receive green texts along with phone calls.

Depends where it is located

It could be the small microphone for noise cancelling or it could be as pointed out above the hole to eject the sim card

I'm with MichelPM. What's the point of a support forum if everyone would know things?

ALSO-

Read the question.

i wish people would pay attention before answering a question. Everyone knows what a sim card slot is.

You might have a Cellular iPad. you can install a SIM for cellular connection.