Yarn bombing is a form of street art made by covering objects in public space with colorful knitted or crocheted patches. It is also known as guerilla knitting. The technique was first practised in Texas, US, but has spread all over the world.
Yarn bombing is a way of reclaiming and personalising public space with crafts.
According to Wikipedia (https://en.wikipedia.org/wiki/Yarn_bombing), yarn bombing originated in Texas, US around 2005, as a way for crafters to make creative use of their leftover yarns and unfinished pieces.