According to the ISO/IEC 27003:2017 and various ISMS implementation maturity models (e.g., COBIT, CMMI), a “Defined” maturity level implies:

“Processes are well-characterized and understood, and are described in standards, procedures, tools, and methods. These are communicated through training and organizational policy.”

This level ensures repeatability and consistency. It is higher than “initial” or “basic” maturity where ad hoc approaches dominate but does not yet include automation (which would fall under "Managed" or "Optimized").