U Chart

An attributes control chart used with data collected in subgroups of varying sizes. U-charts show how the process changes over time, measured by the number of nonconformities per item or group of items.

Unplanned Downtime

Unexpected or unscheduled interruption in operations due to circumstances such as breakdowns, component failures, systemwide failures, power outages, material shortages, staffing shortages or other.

Upstream Processes

The process that supplies the next process downstream. The ultimate upstream point is the first process and the ultimate downstream point is the customer. Upstream processes can be internal or an external supplier.


The time during which a machine, process or system is in operation.

User-centered design

An iterative design process during which designers focus on the users and their needs in each design phase. Design teams involve users throughout the design process using a variety of research and design techniques. The aim of user-centered design is to create products that are highly useful and accessible to users. Abbreviated UCD.

User story

The description of a small, self-contained unit of development work designed to accomplish a specific user goal. A user story is written from the user's perspective. The typical format is, “As a [user persona], I want to [perform specific action] to accomplish [specific goal].”

U-Shaped Cell

U-Shaped Line

A work area with the processes and equipment arranged in sequence in a U-shape. A U-shaped line allows people to work in a circular motion, finishing at the starting point of the cell, eliminating the waste of walking back from the end of a straight line. The U-shape allows either a single or multiple operators to staff the cell based on customer demand and pace of work. A U-shaped cell also supports visual management and communication, because the opening of the U-shape acts as both the material and information input and output points.