Discuss as:

Motion blur

Nicky Loh / Reuters

Dancers perform during a dress rehearsal of Cloud Gate Theatre's "Water Stains On The Wall" in Taipei November 18, 2010. The latest dance production created by Taiwan choreographer Lin Hwai-min will premiere on November 19 in Taipei.

Carlos Barria / Reuters

Hong Kong's Au Sin Ying fights China's Tan Xue during their women's individual sabre bout at the 16th Asian Games in Guangzhou, Guangdong province, on November 18, 2010.

From Photodictionary.com:

Motion blur refers to the effect in a photograph produced by photographing an object that is moving quickly. The subject is moving so quickly that the shutter cannot freeze the action. Motion blur can be avoided (or obtained) merely by adjusting the shutter speed. Note: Motion blur should not be confused by camera shake.