For as long as people have been riding bikes, wheel systems have come in two styles: clincher and tubular.
A clincher wheel system uses a tire and rim that has a bead interface but relies on the air pressure in the inner tube to hold the tire on the rim bead. The tube also offers added support for the tire, allowing the tire to be thinner and lighter by itself.
The tubular style is a bit different in that the tire, tube and valve are all one. The rim has a concave shape but no bead. Instead, the tire is either glued or taped to the rim. Since the tire, tube and valve are all one unit, they can be specifically designed for certain conditions or ride characteristics. Professional cycling has relied on tubulars for many years because of this. The downside to this system is the tires are very hard to change if you get a puncture or wear them out, and there are few options when it comes to repairing a puncture.
However, in the last five years the road world has begun to embrace the tubeless technology that the mountain bike community has relied on for over a decade. While the demands of a road and mountain tubeless system are very different, they both rely on a specifically designed airtight tire and rim interface with some sort of sealant and valve. Like clinchers, tubeless tires have a bead.
Thanks in large part to the gravel market, tubeless is becoming more popular because it eliminates pinch flats and allows manufacturers to design a tire with specific traits without the age-old complications that tubulars can have. Tubeless tires are still not without their hassle, but things have improved significantly in recent years. Plus, if tubeless is offering too many issues, you can just quickly remove the valve and use an inner tube.
It’s important to remember that while all tubeless tires use clincher rims, not all clincher rims are tubeless-ready. If you want to run tubeless, be sure you have a tubeless-compatible rim.