What does it mean to "Follow" someone on Social Media?
To follow a user in a social media website means to subscribe to receive notifications when that user posts a new post. In general, you would have a list of posts that come from users whom you follow called "feed," "dash," or "timeline." Every time someone whom you follow posts something, the post appears in your feed.
Someone who follows a user in a social media is called a "follower." The more followers you have, the more people will be notified when you post something new. Two people who follow each other are called "mutual followers," or "moots."