Any individual who rarely or never initiates social interaction on their own initiative, but instead attaches themselves to more social people when they run into them and hangs out with their friends.
This phenomenon is often most common in schools and small towns, especially in teenagers and young adults; particularly if they've either recently switched schools or moved to a small town.
This can often act as a behavioral crutch, in which the Social Remora in question satisfies their social needs without learning how to fulfill them on their own, stagnating their social development. This resulting social stagnation often manifests itself as difficulties in dating relationships, as the Social Remora lacks the social experience to feel comfortable interacting with another person on their own initiative.
Remedies for Social Remoras:
The best way to stop being a Social Remora is to start hanging out with people by your own initiative. Get your friends' phone numbers and ask them to hang out sometime; see a movie, play board games, hang out at a park, share your favorite tv shows/movies, even study for school. Not only will this give you a social life, but it will provide you with basic interpersonal skills, making you more comfortable hanging out with other people in a one-on-one basis, and less awkward when you try to date people; an activity for which interpersonal skill are usually a mandatory prerequisite by nature.
Jane: "That Billy kid's pretty funny, but he's really not as social as I thought he was. He's always up for hanging out when someone asks him, and always shows up to parties and such when invited, but he never calls anyone to hang out on his own."
Mary: "I've noticed that too; he is kind of a Social Remora, isn't he?"
Billy: "Arg! I really like Jane, but we only ever hang out between classes at school, and when I run into her at parties, she's usually with her friends whom I don't know. I want to ask her out, but since I don't hang out with people on my own initiative often, I'm worried that even if she said yes, I'd be really awkward and off-putting on a date. Why do I have to be such a Social Remora?"