An "alumni database" is a collection of information about people who have graduated from a particular school or institution. It helps keep track of graduates' contact details, careers, and other relevant information. Full definition
Between hosting seminars, interacting with local companies, and constructing alumni databases, postdoctoral organizations are beginning to help postdocs develop the networks they need to transition to their next position or career. (sciencemag.org)
Many colleges have alumni databases specifically designed for networking purposes. (thebalance.com)
You can also search your college alumni database to see if anyone worked there. (job-hunt.org)