The ring carried by Bilbo and Frodo in J.R.R. Tolkien’s stories is the One Ring.
Sauron forged the One Ring in the fires of Mount Doom during the Second Age. He placed much of his power into it so that he could dominate the other Rings of Power and control their bearers. The inscription on the Ring is written in the Black Speech of Mordor.
Bilbo finds the Ring beneath the Misty Mountains after Gollum loses it. He later gives it to Frodo, who carries it during the quest to destroy it. The Ring can make its wearer invisible to ordinary observers, but its deeper importance is its connection to Sauron’s power.
The One Ring is distinct from the Elven Rings, the Seven Dwarf-rings, and the Nine Rings given to Men. Those objects belong to the wider Ring legend.