Complex sentence: The lesser pelvis (or "true" pelvis) is the space enclosed by the pelvic girdle and below the pelvic brim: between the pelvic inlet and the pelvic floor.
Split into simpler sentences: The lesser pelvis (or "true" pelvis) only includes structures inferior to the pelvic brim. It is the part of the space enclosed by the skeleton of the pelvis which is situated between the pelvic inlet and the pelvic floor.