What does that mean? A “constituent” means that you live in a particular legislator’s district, and therefore, can vote for them (or not). Even though we are all “technically” served by all legislators, we can only vote for those in whose district we reside.
BUT, something that is annoying to many members and staff is when people refer to themselves as a constituent and say they live in the district when they don’t. You have every right to lobby those who don’t physically represent you – just don’t make the mistake of saying you are a constituent when you are not. It undermines your credibility.