To identify customer type (economy, marketing etc)?

Hi, could you please help me with a question on identifying customer types?

For customer always come and buy, we call them loyal customers.

There’s a type of customer, they come and buy for a subsequent period, then disappear for a subsequent period, and come back again for another subsequent period.

The pattern repeats, and there’s no way to tell when they come or leave.

Is there a name of this customer type? How to describe this type of customer?

Thank you.