USL(upper specification limit)

the highest value of a product dimension or measurements of a process.

Upper Control Limit

A horizontal line on a control chart(usually dootted) which represents the upper limits of process capability.

upper confidence

the larger of the two numbers that form a confidence interval.

Unit

In manufacturing, a unit can be a final assembly, a subassembly, or a component.  In non-manufacturing a drawing, a purchase order, or a typed document can be a unit.

uniform distribution

a distribution in which all outcomes are equally likely.

Uncensored data

All sample dta have failed or have a reading

UCL(upper control limit)

for control charts: the upper limit below which a process statistic(x bar, R, etc.) must remain to be in control.  Typically this value is 3 standard deviations above the center line.

u-chart

for attribute data: a control chart of the average number of defects per part in a subgroup.