This is a box of ten 25ft spools of solid-core wire. The wire is easy to solder to, and when bent it keeps its shape pretty well. We like to have a few spools of this stuff around which is why this set is quite nice! We suggest picking up some wire strippers to match. Wire gauge is 22 AWG, which we've found is the best all-around gauge, and it works best with breadboards and perfboards but also fits nicely in terminal blocks.
The box has a plastic dowel rod to hold the spools in place and let them spin, and there are little punch-outs you can pass the wire through so it'll stay nicely organized.
Adafruit Product Page: https://www.adafruit.com/products/3174