In short, social media is a way for people to interact with their friends and family (or strangers) on the internet. Usually this is done through a website where people have the ability to create accounts with avatars and personal profiles (Facebook, Twitter). Many times they also have the option to display their personal profiles to other users. Others may prefer forum-type websites where users post in threads (Reddit, 4chan). Using these accounts, they can communicate with other users, post personal information, and share other types of media.
Blogs can be considered a form of social media because many platforms allow readers to establish a presence on the blog. For most blogs that are hosted by an individual or an organization, this usually means that readers have the ability to comment on posts, either anonymously or not. Those who host their blogs on websites like Tumblr and WordPress can interact with and follow other bloggers. This type of social media can lead to users making connections more than something like Facebook because they have the ability to bond over common interests without revealing personal details about their non-digital lives.