Critical threshold

Critical threshold, a notion derived from the percolation theory, refers to a threshold, that summons up to a critical mass. Under the threshold the phenomenon tends to abort, above the threshold, it tends to grow exponentially.

In cases where the phenomenon is not sudden and takes time to operate, in the form of a transition phase or phase transition, we talk about a critical phase more than a critical point that would mark a clear threshold.

Examples
This process is common in physics (nuclear chain reaction), chemistry, biology, ecology, but also in economics. Many economic processes, from product life cycles or economic development to stockmarket bubbles follows also such a succession of phases, first building up pressure, then breaking through.

A specific example in economic geography / spatial economics
In some locations, resources and competences amass and develop a science and high tech oriented cluster like the Silicon Valley, or recently Bangalore software center and AMD´s chip-plants, FAB's, in Dresden, F.R. Germany.