Plain English Meaning
A turbine engine compressor built in two separate rotating sections that spin at different speeds. Air passes straight through both sections, getting squeezed harder at each stage before reaching the combustion chamber.
Full Definition
A turbine engine compressor design with two independent rotating assemblies (spools) arranged on concentric shafts, each driven by its own turbine stage and free to rotate at different speeds. Air flows axially (parallel to the engine's centerline) through both compressor sections in sequence: a low-pressure compressor (N1) followed by a high-pressure compressor (N2). Each spool self-adjusts its rotational speed to match airflow demands, improving efficiency, compression ratio, and engine across a wide operating .