Senses
内线/ 內線 insider; internal connections
a person or group planted inside an organization to gather information; internal contacts or personnel relationships used to gain an advantage (e.g., inside information)
内线/ 內線 telephone extension
an internal telephone line within an organization or building, usually controlled by a switchboard
内线/ 內線 interior lines
a line of communication or battle front that is inside the circle of an enemy's encirclement