A portfolio is a collection of investments held by an individual or organization. It can include a variety of assets such as stocks, bonds, real estate, and cash. The purpose of a portfolio is to diversify investments and manage risk. Portfolio diversification is the process of spreading investments across various asset classes and types in order to reduce the overall risk of the portfolio. By holding a mix of investments, a portfolio can potentially produce a better return while minimizing the impact of any single investment's performance on the overall portfolio.