Bundleware... a meticulous method of storing multiple stamps of the same type/design/denomination, prevalent in the early-to-mid part of the 20th century, but now seemingly out of vogue.
Individual bundles are usually all of the same stamp design, grouped in 50s or 100s, bound together with string or paper wrappers (like currency wrappers from the bank if you get new bills 20 or 50 at a time).
Most bundleware I've encountered is 1920s-1950s U.S. definitives, usually only of interest if you are a flyspecker or cancel/precancel collector, as the stamps are almost always of nominal value. Finds are possible if one is perseverant, but going through the stuff is a tedious task at best.
I've also seen bundleware from Canada, the UK, France, and Germany, again usually from the early-to-mid 20th century.
This particular group of bundleware is a bit more esoteric and more up my alley: The camel and postrider stamps of Sudan.
Should make for some fun cancel and flyspecking hunting!