Definition
Training arranged so that one person can work several stations; it is the means and the multi-skilled worker is the result, with progress and gaps shown on a cross-training matrix (rows are people, columns are stations).
In detail
Cross-training is not about making people do more work but about letting the cell be restaffed as demand changes: when takt changes or somebody is away the line still runs to standard work. The matrix is its management tool — rows are people, columns are stations, and each cell is divided into four quadrants showing training progress. What to look for is the column with only one qualified person (a single point of failure) and the row that has not moved for months (a training plan nobody owns). When a second cell is added the plant-wide matrix must be updated, or interchangeability exists only in the first cell. Qualification is not attending a class; it is having worked that station alone to standard work.
Example in practice
Two of six stations in a cell have only one qualified operator, and the line stops the day one of them is on leave. The team builds a three-month rotation from the matrix, one new station per person per month, and after three months every station has at least two qualified operators.