In order to conserve memory, transients were small modules that supported a specific task, and were swapped in and out of memory. The concept of transient area is part of Mythical Man-Month's discussion on design and the use of main memory.
To optimize memory efficiency, transients were compact units that focused on one particular task, and were inserted and removed from memory as required. This concept about a transient area is mentioned in Mythical Man-Month as part of its examination of design principles and main memory utilization.