A variable that appears in a calculation only as a placeholder and which disappears completely in the final result. For example, in the integral
 |
is a dummy variable since it is "integrated
out" in the final answer. Any variable name other than 
could therefore be used in the above expression, e.g., 
, 
, etc.
Dummy variables are also called bound variables or dead variables. Comtet (1974) adopts a notation in which dummy variable appearing as indices in sums are denoted by placing a dot underneath them (i.e., indicating them with an underdot), e.g.,
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(Comtet 1974, p. 33).
