Definition
A portfolio is the total collection of all your investments — stocks, funds, bonds and other securities. The term comes from Italian "portafoglio" — a folder for carrying documents. Today the portfolio carries your financial values.
Example: You own Equinor (25%), DNB (20%), Mowi (15%), a global index fund (30%) and cash (10%). That is your portfolio.
Diversification: A well-composed portfolio spreads risk so that one bad investment does not destroy the whole. That is the portfolio most important function.
"A wise investor does not build one house — they build a city. Many strong investments are stronger than one perfect one."— Florence Scovel Shinn