What is the difference between A2P and P2P SMS?

A2P (Application to Person)

A2P SMS is one where an SMS message is sent from an application — typically a web app to a mobile subscriber. These text messages can also be sent in the other direction (from a mobile subscriber to a web app). This is known as P2A (person-to-application) messaging. The common use cases of A2P are alerts, notifications and marketing messages such as banking updates or flight alerts.

P2P (Person to Person)

P2P SMS is where an SMS message is exchanged between two mobile subscribers. These use cases include group chat applications, anonymous dating applications, SMS on virtual phone numbers like Google Voice, etc.