process (noun) — something going on; a natural phenomenon marked by gradual changes that lead toward a particular result.
The term recurs across Brian's work as a contrast to activity — the state of performing a specific function. Where activity-thinking treats a thing as already-defined and complete, process-thinking treats it as ongoing and revealing. The distinction is developed in 📝A Process, Not An Activity, and Ryan Holiday's essay Here's the Strategy Elite Athletes Follow to Perform at the Highest Level catalogs the same lens in elite sports — coaches and players who "trust the process" rather than chase a specific outcome.