When used to describe jewelry, the word stone can be misleading.  Technically, a stone is a type of material (gemstone).  You can have glass, metal, plastic or stone beads.

However, in the costume jewelry world, 'stone' is an abbreviation for rhinestone.  Swarovski crystals are frequently called stones.  Some people use the world stone and bead interchangeably.  They will describe plastic beads as plastic stones or just as stones. Make sure  you know what you're buying when you look at 'stone' jewelry.