Hello Harshit
When we speak about point to point and point to multipoint we are primarily talking about the different types of topologies that exist using Frame Relay.
Strictly speaking, a point to point connection is one that is created between two routers using a serial technology, as you correctly state. Frame Relay is such a technology. Now if you connect two routers together using Frame Relay this is a point to point connection. However, you can also create two point to point connections over Frame Relay, where you have a single Hub router connected to two spoke routers like so:
What makes this topology point to point is that each link has a separate subnet. The S0/0 interface of the hub has two subinterfaces, each one on a different subnet, connected to each individual spoke.
Now a point to multipoint scenario is one where all three routers have IP addresses in the same subnet, still using Frame Relay as the technology. Now this seems strange, because we’re using a non-multiaccess technology, how can we have three routers in the same subnet? Well, Frame Relay is able to make this happen by “simulating” multicast within a multiaccess technology. And this lesson describes how you can make OSPF, which requires multicast, to function in an inherently non-multicast non-multiaccess network.
You can find out more about point to point and point to multipoint topologies at the following lessons:
I hope this has been helpful!
Laz