Code 11
A dense numeric barcode from 1977 used almost solely to label telecom equipment.
Intermec devised Code 11 (also called USD-8) in 1977 as a compact symbology for the digits 0–9 plus the dash. Each character is built from three bars and two spaces, and one or two check digits (called C and K) catch read errors. The name refers to the eleven encodable characters.
It found a single niche and stayed there: labelling telecommunications equipment, especially telephone exchanges and cabling, where density mattered more than being readable by everyone. Outside that trade it is rare, and newer applications reach for Code 128, which packs digits and letters tighter still. It is read by ordinary barcode scanners that support the symbology.