Bring Your Own Tools (BYOT) is a contradictory approach to living off the land in which attackers bring their own tools to use during offensive operations. This may include writing tools to disk and executing them or operating in memory only.
The idea is that EDR and other security tools know about living off the land and monitor these tools.
Bring your own tools is similar in concept to bring your own island, but typically refers to bringing one or a handful of tools versus an entire arsenal of utilities.