Basement egress is the ability for occupants to escape from a basement in a way other than the stairway to the upstairs.  This gives occupants more than one option should there be an emergency that requires fast and safe evacuation.  Modern building codes now require that basements that have a finished living area have more than one way of exiting a basement.

Basement egress can be a sliding glass door for a walk out basement.  Or if the basement is completely surrounded by soil, then an egress window must be included.  With that window is an egress window well that has a ladder included.