The presence of the necessary capacity, availability and flexibility in terms of the 4 M's: people, machines, materials and methods. If this basic stability is absent from a process, then improvements cannot be implemented or sustained. 

A process that possesses basic stability is capable (able to reliably produce good parts, but not yet capable of Jidoka at every step), available (can produce when needed and according to the rhythm of the branch time) and flexible (able to convert after a few items, but not yet talking about every-product-else-interval (EPEx)). 

Basic stability is necessary for effective Just-in-Time (JIT) production. This often involves an implementation cycle of basic stability - flow - branch time - pull - heijunka. The cycle is repeated as many times as necessary.