A2P and P2P messaging are two different approaches to SMS messaging.
P2P, or Person-to-Person messaging, is when one mobile phone user sends a mobile message to another. This is typically seen in conversational messages sent between people.
A2P, or Application-to-Person messaging, is when mobile users receive messages from an application. This includes but limited to multi-factor authentication messages, notifications, reminders, and marketing messages.
Different countries impose specific restrictions on A2P and P2P traffic. For example, P2P messages in the US and Canada should be sent via long codes, while A2P messages in APAC should be sent generally via short codes or Alphanumeric Sender IDs.