名詞 placeholder:

1. a person authorized to act for another
   同義詞：proxy, procurator
2. a symbol in a logical or mathematical expression that can be replaced by the name of any member of specified set

place.hold.er

n.（名詞）
One who holds an office or a place, especially:
占位的人：處于某一職位或位置的人，尤指：
One who acts as a deputy or a proxy.
代理：做代理或委托的人
One who holds an appointed office in a government.
任職：在政府機(jī)構(gòu)被委認(rèn)某職的人
In a mathematical or logical expression, a symbol that may be replaced by the name of any element of a set.
占位符號：數(shù)學(xué)或邏輯用語，可以用其它元素的名稱代替的符號
In the decimal form of a number, a digit that is not significant.
占位符號：在一個數(shù)的小數(shù)形式中，沒有意義的數(shù)字