Directly adjacent locations of processing steps for a product. Parts, documents etcetera can be processed almost in continuous flow, either one at a time or in small batches, which are maintained throughout the entire sequence of processing steps. 

A U-shape is the most common cell shape because it minimizes walking distances and allows operators to perform different tasks. This is an important consideration in Lean production because the number of operators in a cell changes with changes in demand. A U-shape also makes it easier for the first and last steps in the process to be performed by the same operator, contributing to a stable work rate and even flow. 

Many companies use the terms cell and line interchangeably. 

Some people believe that, from the operator's point of view, material should always flow through the cell from right to left, because more people are right-handed and it is more efficient and natural to work from right to left. However, there are also many efficient processes that flow from left to right. It is best to assess which direction is more logical on a case-by-case basis. 

Below is an example of a U-shaped cell:

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