lobby-n; 3 Senses

Sense Number 1: the public foyer or entry hall of a public building

Commentary: LOBBY[+building][+public][+room][+public][+foyer]
NOTE: implies a public meeting area in a larger public place

The hotel lobby had marble floors and giant chandeliers.
We are all meeting in the lobby at six this evening.
This restaurant recently renovated its lobby.

WordNet 3.0 Sense Numbers: 1

Sense Number 2: political interest group, organized activists

Commentary: LOBBY[+group][+people][+activist][+political][+organized]
NOTE: the people who engage in the political activities (Sense 3)

Members of the anti-abortion lobby are speaking with senators today.
He is a member of a lobby that represents the tobacco industry.

WordNet 3.0 Sense Numbers: 2, 3

Sense Number 3: the act of exerting political pressure by an activist group

Commentary: LOBBY[+activity][+political][+pressure]
NOTE: the activities which the people (Sense 2) are engaged in

He mentioned the recent lobby of Congress by retirees.
There have been several lobbies by unions against the proposed trade bill.

WordNet 0.0 Sense Numbers: 2a