Yarn bombing is a type of graffiti or street art that employs colourful displays of knitted or crocheted yarn or fibre rather than paint or chalk. It is also called wool bombing, yarn storming, guerrilla knitting, kniffiti, urban knitting, or graffiti knitting.

Graffiti is art that is written, painted or drawn on a wall or other surface, usually without permission and within public view. Graffiti ranges from simple written words to elaborate wall paintings, and has existed since ancient times, with examples dating back to ancient Egypt, ancient Greece, and the Roman Empire.