This is a box of ten 25ft spools of stranded-core wire. Stranded-core wire is best used for wiring jigs where there's bending or movement expected. It also works well with terminal blocks. It's not great for use with breadboards (without tinning). The wire is easy to solder to, and when bent it keeps its shape pretty well.
This set is not good for breadboarding!
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/3175