The EAI can be divided into Sources, Bridges and Destinations. BizTalk Adapter Service (BAS) – can be considered as a special type of destination – relay end point.
Source is from where you want to receive the message (equivalent to Receive Port in BizTalk on premise)
Destination is where you want to send the message (equivalent to Send Port in BizTalk on premise)
Bridge connects Source and Destination and provides various stages to modify, transform, enrich the message (equivalent to Pipeline in the BizTalk on premise)