What does 3 IVF cycles mean?

When the doctor says for your age group almost 90 percent in 3 IVF cycles. Does that mean 3 transfers or by the 3rd ER? & if it’s 3 ER’s how are they getting that data because everyone gets different number blasts? I told my husband it means 3 transfers but he’ll tell me no IVF cycles like 3 ERs. But again how many transfers then? If that makes sense lol