A whole number. A great many economic variables, such as the number of firms in an industry, must be whole numbers: this is known as the integer constraint. Economists often find it convenient to igonore the integer constraint, and treat economic variables as though they were continuous. Even the national income can in fact only vary in steps, equal to the smallest unit of currency, but this is so small that it is felt that the convenience of being able to use calculus and other properties of continuous numbers outweighs any possible inaccuracy due to treating income as a continuous variable.

• undated security
• under-capitalized
• under-developed country
• under-funded pension scheme
• underlying rate of inflation
• under-subscription
• under-valued currency
• underwriting
• undistributed profits
• UNDP
• unearned income
• unemployable
• unemployment
• unemployment benefit
• unemployment rate
• unexpected inflation
• unfair competition
• unfair dismissal
• unfunded pension scheme
• unified budget
• uniform business rate
• uniform distribution
• union
• unionized
• union/non-union wage differential