Some loans feature an interest only payment option that allows you to decide monthly how you would like your mortgage payment to be applied. To reduce outlay for a couple of months, you can choose to pay interest only. For the following months, you can make full payments to cover both principal and interest.
This type of loan was popular before the housing crisis and has become much less common in recent years. Today, it is more likely to find this feature on an adjustable rate mortgage than on a fixed rate mortgage. It can be a helpful feature in the right situation, but its ramification need to be fully understood and it should be used with extreme caution.