The narrow inner ring on a standard darts board is called the treble ring, and it scores three times the segment number.
For example, a dart in the treble 20 segment scores 60, the highest score possible with one dart. The ring lies between the bullseye area and the outer double ring. Its narrow width makes accurate treble hitting one of the central skills of competitive darts.
Players often call the treble ring the triple ring, and both expressions are understood. “Treble” is especially common in traditional British darts terminology. The word does not mean that every dart in the ring scores three points; it multiplies the number printed in that segment by three.
This ring should not be confused with the outer bull, which is a separate circular target worth 25 points. The bullseye centre is worth 50 and is treated as a double for checkout purposes.