Obtainium and "good stuff"
Deep into the earliest days of tinkering history there have been extra things, bits, bobs, whoozits, and whatzits galore. Even the term Tinker used to refer to someone who was capable of repairing worn cookware and other household odds and ends. Used, or cast off things often take on a second or third life in ways they weren't originally intended for, and Freeside has such things in spades. To avoid being overrun and buried in a dragon's hoard of half-broken VCRs, mystery car parts, and the like, it's important to know when something might ever practically be reused. Hence the concept of "Obtainium".
In scifi (and sometimes engineering) Un-obtainium is a mystery material or part that simply can't be found. Obtainium on the other hand is materials that someone has no immediate need for, but which still has plenty of use for others down the line. Order a 4 pack of microcontrollers because it costs the same as a 2 pack you need? Toss the rest into Obtainium (in the right place please).
Conversely there is "Good Stuff". Good Stuff is things that look like they could be reused and should be kept, and maybe they could be, perhaps for an art project, but most likely they'll collect dust for years and years and take up room without being of any use. Good Stuff has a allure and power that can and has made members pull it from the dumpster time and time again, often calling those in it's thrall to bellow "WE CAN'T THROW THIS OUT! THIS IS GOOD STUFF!". Anyone can be taken in by the siren's call of Good Stuff, and different bits of refuse call to different people.
Learning to tell quality Obtainium from Good Stuff is a lifelong exercise in futility as it exists as an overlapping spectrum. For a primer on making this distinction, learn from George Carlin: https://www.youtube.com/watch?v=MvgN5gCuLac