Flagstone is not a particular type of stone. Rather, it refers to any stone that splits into flat pieces, usually irregular in shape.
Flagstone implies a flat stone that is irregular in shape.
Paver refers to a flat stone that has been cut or broken into some rectangular or square shape.
Bluestone, a hard sandstone from Pennsylvania and New York. It comes in many different forms and sizes, has a very warm color palette of greens, browns and blues, and naturally has a very flat cleft surface. And considering the stone’s quality and durability it’s very reasonably priced.