The portion of the message quoting the message one is replying to. Usually 4 lines is sufficient to remind the recipient what one was talking about. Most offline readers will indent these or place them in different colors, with proper configuration of the offline reader or editor. The actual message itself. A funny or political saying, usually short.
Some editors eliminate the tagline, so the origin line doubles as a tagline.
Echoes are also known as conferences or sub areas. Local echoes are only on one or two bbs's in a given area. Another type of local area might be a User Chat or Forum area. This one is only readable by users of that system, and is usually a place where one user can leave another user a message. A regional echo is an echo that is carried only in one net or region.