OSINT (Open-Source Intelligence) is reconnaissance that uses publicly available information. OSINT relies heavily on social media platforms and search engines to find information.
Threat Intelligence Providers are organizations which conduct threat research and provide their findings to clients. The provider research is often ingested as intelligence threat feeds that can be used in SIEMs.
Some industries have Information Sharing and Analysis Centers which are places to share threat intelligence and best practices. These are often specific to a given industry or sector, such as aviation or finance.
Cybersecurity emerged and evolved over the course of decades. The conflict between attackers and defenders drives the constant evolution of cybersecurity.