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A mentarium, from mental + planetarium or terrarium is one's mental landscape, which may be limited to the (psychological) brain or extend beyond it, perhaps spiritually or aporinically. The term can be used as an equivalent to system, but some systems may have realities outside their mentarium, which are only connected to the mental landscape rather than immersed within it, and mentariums (also mentaria) can contain more than one system, whether that be multiple systems or non-system but mentally-immersed realms.
Mentariums can have any number of functions and properties. In cybratien collectives for example, the mentarium and its functions - psychological, spiritual, aporine, and any others - are governed by a set of natural but malleable laws called the OS, and maintenance may be required to keep the OS - and thus the mentarium as a whole - running smoothly.