On purchasing an under-construction property, your bank may link the disbursal of home loan to the construction stages of the property. In such a scenario, you will either be asked to pay pre-EMI OR given an option to choose between pre-EMI and full EMI payments.
An Equated Monthly Instalment (EMI) consists of Principal and Interest components. Pre-EMI is only the interest portion of the disbursed loan amount that you pay until the full disbursal is done by the bank to the builder.
Your EMI payments start after the pre-EMI phase. Until then, you don't repay any principal loan amount. Some banks allow you to pay full EMI even when the disbursal is being done in stages.