speed lines
A type of motion lines that indicate fast speed. Usually drawn as a large number of lines surrounding the character, or encompassing the entire background.
When used directly on objects, esp. in the foreground, these may be accompanied by motion blur effects.
Not to be confused with emphasis lines, which do not indicate motion, but rather are used dramatically to draw attention to a specific part of the image.
See also
This tag implicates motion_lines (learn more).