Portfolio management is related to the security markets.
In Portfolio management a person or a group of person or company will look out al your holdings (Equities,MF,Derivatives,Capital etc).
While doing portfolio management they will take care of all the securities which belonged to you. they will suggest you when to Enter in a stock or a MF, When to exit.
They will also tell you about Market trends, other way of investments.
In a nutshell Portfolio management is a art to taking care of someone else Property/securities and in return get some percentage of money from the person

Portfolio means an Investor with his limited money buys various shares.This is one kind of balance process. for example.
25 percent for blue chip company shares such as Reliance,Herohonda etc.
These shares are kept like assets
25 per cent for long term shares ,these shares are sold in boom time and repurchased at crash time.
25 per cent for short term investment, these shares likely to change with govt.policies,geopolitics, quick action in buying and selling is required for this.
25 per cent for IPOs,Right issues, etc.
In this manner your total money is divided into various groups and managing them is called portfolio management.