It's a collection of your modelling pictures. How many pictures you need varies. You should only keep strong pictures, you are only as good as your worst picture! Models should aim for quality not quantity! Avoid using 2 pictures of the same shoot (same look) Black and White is the favourite of the industry. 9 by 12 inches are the standard size. Your agency will require you to buy an 11 by 14 inches for their book (portfolio). A basic but versatile portfolio would have a casual head shot, styled head shot, body shot (conservative swimsuit or lingerie), a fashion shot (sexy) , action shot, an editorial shot and even a catalogue shot. As you gain experience replace the older pictures with newer one. Keep your best picture at the end to leave a lasting impression! Do not wear jewellery for those prints, it takes the attention away from you. The wrong choice of undergarments may show panty line or bra straps and will distract the viewer (on the job, or in interviews it can mean the difference between looking professional or not). Tailor your portfolio for your strengths and the type of modelling you are doing.

Project Portfolio Management (PPM) is a management process designed to help an organization acquire and view information about all of its projects, then sort and prioritize each project according to certain criteria, such as strategic value, impact on resources, cost, and so on. The objectives of PPM are similar to the objectives of managing a financial portfolio:
1) To become conscious of all the individual listings in the portfolio
2) To develop a “big picture” view and a deeper understanding of the the collection as a whole.
3) To allow sensible sorting, adding, and removing of items from the collection based on their costs, benefits, and alignment with long-term strategies or goals.
4) To allow the portfolio owner to get the “best bang for the buck” from resources invested.