Having essential capability, availability, and flexibility in the 4Ms -- manpower, machines, materials, and methods. A lack of basic stability in a process prevents improvements from either occurring or being sustained.
A process with basic stability is capable (able to reliably produce good parts but short of jidoka at each step), available (can produce when needed and at a pace with takt time), and flexible (able to change over a few items but short of every-part-every-interval (EPEx)).
Basic stability is required for the effective functioning of just-in-time (JIT) production, which often follows an implementation cycle of basic stability—flow—takt time—pull—heijunka. The cycle is repeated over and over as needed.