As applied to operations management, it is the condition in which the process times for each operation are approximately equal and the work flows steadily or at a desired rate from one operation to the next.
Many in industry focus on establishing balanced lines as an objective in and of itself. A balanced line is not an objective for production or projects. The objective for a project is usually ontime delivery at minimal cost with no safety incidents. There are very many instances where having unbalanced resources in a project is the most effective way to achieve ontime delivery at least cost.