noun
glass bead; glass marble; glass sphere
Refers to small glass balls used as marbles, beads, or decorative spheres. The context usually makes the specific type clear.
子供の頃、ガラス玉を集めていた。
When I was a child, I collected glass marbles.
そのネックレスには青いガラス玉が使われている。
Blue glass beads are used in that necklace.
ビー玉 specifically refers to the small glass marbles used in children's games, while ガラス玉 is a broader term for any glass bead or sphere.
Compound of ガラス (glass, from Dutch 'glas') and 玉 (ball, bead).