A concept from Vernor Vinge's SF masterpieces A Fire Upon the Deep and A Deepness in the Sky.
In Vinge's universe the speed of light isn't constant, but gets faster the further away from matter you go. Down near the cores of galaxies, things don't work at all because light moves too slowly. Out/up on the galactic periphery, technological artefacts can be constructed which have behaviours and abilities indistinguishable from magic.
See also The Singularity
How is this Tcl related??? RS: Then context in which slow zone was first mentioned suggests that Tcl is not in the slow zone - pretty "far out", rather...
Yep, and even more specifically that xotcl is not from the slow zone ... exo-tcl.