What is a Portfolio?

Portfolios are used to provide evidence to an employer of your skills, talent, accomplishments and abilities. They are a showcase of your chosen work that best demonstrates your creative potential, or what ever you think the employer is looking for.
Portfolios are concrete evidence that presents your professional and personal achievements. Types of portfolios are, ring bound file, printed, online, CD, DVD, Presentation. Each type comes with it's advantages and disadvantages, you decide on which best suites the clients needs. (i.e DVD is easy to carry, online for over seas etc)
Example of an online portfolio

Online portfolios are good in that anyone from across the world can view your work. Negatives are that there are so many online portfolios out there that, not all get viewed by potential employers. Also there are different languages in many other countries, so what you put out there might not be able to read.
Digital portfolios are very handy to take to an interview, because they are small (on, CD, DVD, pen drive etc) however disadvantages are, soft wear might not be compatible with the interviewers computer. Also if you are showing print/illustrations etc, it can be hard to demonstrated the 'hand made/ paper quality' when turned into digital copy.
Ring bound portfolios are great for showing your original drawings and any hand made 2D projects. However problems include, weight- can be very heavy, need to take a long time considering mounting and making sure it looks clean and presentable. Also you can't leave it with the interviewer/ possible employer unlike a digital copy.