yarn bombing
noun [ U ] uk/ˈjɑːn ˌbɒm.ɪŋ/ us/ˈjɑːrn ˌbɑː.mɪŋ/
针织涂鸦，毛线大爆炸（一种街头艺术活动，用各色毛线编织的物品偷偷覆盖建筑物的一些部分）
the activity, often done secretly, of covering parts of buildings, etc. with decorative items that have been knitted, as a form of art