Open-source intelligence (usually styled as OSINT) refers to the practice of gathering information from public sources. In a journalism context, this often means knowing how to effectively search the web and social media, for example, to develop background information on someone who has suddenly become a public figure.
The best-known, and maybe only, journalistic organization specializing in open-source investigations is Bellingcat, who have done amazing work with satellite imagery and social media posts, among other sources.
First Steps to Getting Started in Open Source Research - bellingcat
Bellingcat's Online Investigation Toolkit [bit.ly/bcattools]
This one is oriented towards defense and government intelligence, more than journalism, but it’s kinda interesting just to browse anyway!