LinkedIn is a professional networking site with over 175 million members that allows users to create profiles summarizing their expertise and achievements. The document discusses how developing a LinkedIn profile can help users connect with other professionals, find new career opportunities, and stay in touch with colleagues. It also notes that having an online presence on LinkedIn is important because search engines like Google prioritize LinkedIn profiles, and those not in the first few pages of results receive no clicks. The document provides tips on customizing a LinkedIn profile and engaging with the network.