Colloquial term for the entire system of non-sophont machines, databases, programs, etc. that supports and controls the infrastructure throughout most of the civilized galaxy.
This includes basic robots, router programs, low-level maintenance and construction systems etc. etc. In most mid to highly developed systems and in virtually all Inner Sphere systems the mechosystem can equal or surpass the complexity of a naturally evolved ecology. The various levels of sapient ais manage and move through the mechosystem in much the same way organic intelligence manages and moves through the biological world.
Sometimes feral ecosystems can emerge, leading to whole worlds or systems which evolve independent mechospheres outside of any sophont control. These are generally known as botworlds. Examples of botworlds include those in the Surreal Rash, as well as Bothyga M'vau, Stanislaw and Perihelion.