Dark Web
Definition
The dark web is a hidden part of the internet accessible only through special software like Tor. It is notorious as a marketplace for stolen data, malware, and other illegal activities.
The dark web is part of the "deep web" (all content not indexed by search engines). The dark web itself is specifically anonymous and requires Tor or I2P.
For security teams, dark web monitoring is valuable: leaked credentials and stolen company data are sometimes traded through dark web forums.