unconditional probabilityunconditional relative frequencyunconditional relative frequency of eventunconditionallyunconfirmed creditunconfirmed letter of creditunconnectedunconstrainedunconstrained optimizationuncorrelated infinityuncorrelated random numbersuncorrelated random variablesuncorrelated samplesuncorrelated variablesuncountabilityuncountableuncountable setuncoupled systemunctional statementundampedundamped oscillationundamped waveundate periodundefinableundefinedundefined conceptundefined termundefined termsunderunder applied overheadunder flowunder investigationunder the actionunder the action ofundercritical dampingundercut face toothundercut sectionunderdampedunderdamped oscillationunderdampingunderdetermined systemunderemployed economyunderestimateunderevaluationunderfillsundergounderline crackingunderlyingunderlying groupunderlying mapping of a function