A portfolio is a combination of various investment products like bonds, shares, securities, and mutual funds. Portfolio revision involves changing the mix of securities in an existing portfolio by adding or removing assets. This is done to maximize returns and minimize risks. Reasons for portfolio revision include having additional funds to invest, changes in financial goals, or market fluctuations. There are active and passive portfolio revision strategies, with active strategies involving more frequent changes and passive only changing according to predetermined rules. The roles of a portfolio manager include designing customized investment plans, keeping up to date on the market, guiding clients impartially, and regularly communicating with clients.