LinkedIn is a professional social networking site used to connect with colleagues and business contacts. It allows users to build a professional profile, connect with others in their network, search for jobs and business opportunities, and ask and answer questions. The presentation provided an overview of LinkedIn's features and benefits, including how to set up a profile, connect with others, search for people and companies, and get introductions and recommendations. Tips were also shared on using LinkedIn effectively to expand one's professional network and brand.