What is Mission Creep?

Feature creep is sometimes called demand creep or range creep.

Characteristic creep

Right!

Feature creep is sometimes called demand creep or range creep.

Feature creep (sometimes called demand creep or range creep) is that during the development of a product or project, the demand-driven changes or growths are different from the original ones, bringing some product characteristics that were not planned at first, Impact on product quality or schedule. Feature creep comes from a "requirement list" of customer growth, or the developer itself finds opportunities to improve the product. To control feature creep, project management tools such as the requirements stability index (RSI) are sometimes advocated.

Feature creep and expected feature creep are bothersome, like a ghost movie on Halloween. ^[1]