Final answer:
A registered LO in the context of lobbying is known as an in-house lobbyist, which refers to an employee who lobbies on behalf of their employer as part of their regular job duties.
Step-by-step explanation:
A registered LO refers to an individual who is a lobbyist. Specifically, if the question is asking about a registered LO as someone who lobbies on behalf of their employer as part of their job, the most appropriate answer would be:
An in-house lobbyist is an employee who performs lobbying activities as part of their regular job duties for the organization they work for. On the other hand, a volunteer lobbyist is someone who lobbies without compensation or as a part of their employment responsibilities.
Therefore, the distinction between an 'in-house lobbyist' and a 'volunteer lobbyist' lies in their professional relationship with the organization and the nature of their lobbying efforts.