The modeling portfolio is what will get you signed by a modeling agency(s) and hired by clients. Modeling is a first impression business. Your photographs are always seen by the modeling agencies and clients BEFORE you are, so if they don't sell your ability to be an amazing model, they probably will not give you any work.
A modeling portfolio is the collection of photographs that were taken to show the models range and ability. These photographs are submitted to modeling agencies and clients in the hope of getting signed or getting work.
Shooting your modeling portfolio is the most important thing that you will do as a model. Hopefully you make it to the cover of a major magazine some day, but without an amazing modeling portfolio your career will never get off the ground.