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(plāsˈhōlˌdər)

1. One who holds an office or place, especially:
   a. One who acts as a deputy or proxy.
   b. One who holds an appointed office in a government.
2. In a mathematical or logical expression, a symbol that may be replaced by the name of any element of a set.
3. In the decimal form of a number, a digit that is not significant.