Unborrowable stock is the stock that no one is willing to lend out to short-sellers. When shares in a company become unborrowable, the traditional means of short selling them is impossible.

Unofficial strike is union members seizing their work without endorsement from the union and that does not follow legal requirements for the strike. 

Uneconomic growth is economic growth that has negative effect on the society which can become a reason for overall quality of life reducing.

Upside is the potential increase in value, measured in money or percentage of an investment.

Unilateral transfer is a one-way transfer of financial instruments or property from one country to another. 

Unqualified opinion is an independent auditor's judgment on company's financial statements.

Unmatched book is an imbalance occurring when the maturity of bank's assets doesn’t match the maturity of its liabilities on the balance sheet.

An underweight portfolio is a portfolio which does not hold sufficient amount of a particular security when compared to the amount of that security held in underlying benchmark portfolio. 

Underperform is a term defining professional recommendation given when a stock is expected to do a little bit worse than the market return. 

Unrealized gain is a profit that only exists on paper and results from an investment. It is a position that is sold is going to bring profit. Gain becomes realized when position is sold.