The location of processing steps for a product immediately adjacent to each other so that parts, documents, etc., can be processed in very nearly continuous flow, either one at a time or in small batch sizes that are maintained through the complete sequence of processing steps.
A U shape (shown below) is common because it minimizes walking distance and allows different combinations of work tasks for operators. This is an important consideration in lean production because the number of operators in a cell will change with changes in demand. A U shape also facilitates performance of the first and last steps in the process by the same operator, which is helpful in maintaining work pace and smooth flow.
Many companies use the terms cell and line interchangeably.
There is a school of thought that material should flow through cells in a right-to-left direction relative to the operator, because more people are right handed and it is more efficient and natural to work from right to left. However, many efficient processes flow to the left and many flow to the right. Simply evaluate on a case-by-case basis whether a particular direction makes more sense.