How do you define the core?

The core as a general term i use it to describe the entire torso, and specifically but not limited to the mid section. i use the term brace your core with my clients which depending on the exercise can mean any part of the torso. For example while i have them performing a dead-lift i say tighten up your core and not let it move, meaning the spine should remain in neutral, with the movement being performed with the legs. so they would keep their scapula’s squeezed back abdominal area tight as well as there lower back in order to prevent that spine from rounding.