M2M refers to devices communicating with each other on a wired or wireless network. Point to Point (PoP) communications are usually embedded within the hardware at the customer's site. These devices do not necessarily rely on an Internet connection to communicate with each other.
While M2M and IoT (Internet of Things) both refer to devices communicating with each other, M2M refers to isolated instances of device-to-device communication, and IoT refers to a grander scale, synergizing vertical software stacks to automate and manage communications between multiple devices. IoT refers to devices using IP networks with data being delivered through a middle layer hosted in the cloud and, in most cases, require an Internet connection.