Proton sends and receives messages. Messages are transferred between connected peers over links. At the sending peer the link is called a sender. At the receiving peer it is called a receiver. Messages are sent by senders and received by receivers. Links may have named source and target addresses, which can be used to identify the queue messages are sent to or received from.
Links are established over sessions. Sessions are established over connections. Connections are generally established between two uniquely identified containers. Though a connection can have multiple sessions, often this is not needed. The container API allows you to ignore sessions unless you require them.
A connection operates using a transport. A transport is a network communication channel, such as a TCP connection.
The sending of a message over a link is called a delivery. The message is the content sent, including all metadata such as headers and annotations. The delivery is the protocol exchange associated with the transfer of that content.
To indicate that a delivery is complete, either the sender or the receiver settles it. When the other side learns that it has been settled, it will no longer communicate about that delivery. The receiver can also indicate whether they accept or reject the message.