The "Broken Back Seax" is a type of knife or dagger that was characteristic of the Anglo-Saxons, the Germanic inhabitants of England from the 5th century AD until the Norman Conquest in 1066. The name "seax" itself refers to a type of single-edged knife that was commonly used among the Germanic peoples during this time period.

The term "broken back" refers to the shape of the blade. A Broken Back Seax typically has a straight cutting edge for the majority of the blade's length, but towards the tip, the spine of the blade abruptly angles downward, creating a distinctive break in the profile of the blade. This design feature is thought to have provided additional strength to the tip of the blade, making it more effective for thrusting and stabbing motions.

Broken Back Seaxes were versatile tools and weapons, used for various tasks including cutting, slicing, and stabbing. They were often carried by Anglo-Saxon warriors as a sidearm in addition to their primary weapons such as swords or spears. These knives were also frequently used for everyday tasks such as hunting, woodworking, and food preparation.

The Broken Back Seax is an iconic symbol of the Anglo-Saxon period and has been found in archaeological excavations throughout England and other parts of Europe where the Anglo-Saxons had influence.