Meatspace is a neologism that refers to the “physical world” in contraposition to the “virtual world”, which is described by the word Cyberspace.
Somewhat replaced at this point by the terms “IRL”/“OL”, where “IRL” ceased to be interpreted strictly as an initialism for “In Real Life” and actually started being used as a noun to refer to the physical, “offline” world, the word meatspace sprung up somewhere on the late BBS and the Usenet era - the first attested “official” recognition came in 2000 by the Online English Dictionary and its earliest attested usage in 1995[Citation Pending], but anecdotal evidence points that the term goes back to the '80s and picked up traction around the appearance of the Web in 1993. The term then propagated around irc and then on the blogosphere and forums. Its usage today remains sparse, but you can still find some older people (“old” by the standards of the Internet, anyhow) use it in social networks and the like.
The word "Meatspace" actually sucks
It only takes a moment of conscious thought to realize that the word “Meatspace” fucking sucks. A witty, “geeky” reference to the physicality of humans, perhaps inspired by William Gibson's overuse of meaty analogies so as to drive the point home about the crudeness of the flesh in comparison to cyberspace, the end result is a tacky and almost unprofessional word that, in English, clashes in every serious attempt to use it in a formal context and is also essentially impossible to translate in many other languages. There's a reason “IRL” became prevalent, even if it was meant to serve as one of many online abbreviations, the stream of discourse in cyberspace chose to make a noun out of an initialism because the older alternative was somehow even more unwieldy.
A good way to solve the issue of translation is to use more universal prefixes and suffixes, such as those loaned from Greek or Latin - after all, “cyber-” comes from the Greek Kubernes; incidentally, Kubernes only means “driver” or “helmsman” and the word Cybernetics (Kubernetes) ties to this idea of driving or leading a ship, the word acquiring a relation to the concept of a controller - the linguistic-conceptual link from automation to control and to a total virtual space provided by the Internet-at-large1) is visible, but the word now barely holds meaning with its origin.
With proof within this set of terms that etymological coherence is not mandatory, the word “Meatspace” can be changed from ugly, inconsistent (what does “meat space” per se tells us, after all? Without context it's hard to discern its meaning, even when placed against its opposite tern “cyber space”) and untranslatable to just inconsistent (an attribute that proves to be irrelevant so as to only its actual meaning mattering at all), with the usage of more universal terms -in this case, the search for a prefix for the word “space”- that can hold just a modicum of aesthetic sensibility so that it is not as jarring as “Meatspace”.
My personal proposal, avoiding the Greek word “soma” (σῶμα, body) as “somatic space”/“somatospace” remain too ambiguous for their similarity with words in a number of academic fields, centers instead on the Greek word “sarx” (σάρξ, flesh), sufficiently idiosyncratic so as to remain unique for a term and still remain receptive to translation efforts - thus, a word like sarcospace may work better instead2).