wild card

英 [ˈwaɪld kɑːd]

美 [ˈwaɪld kɑːrd]

n. (由持牌人自由决定牌值的)百搭派，变牌; “百搭”式参赛，“百搭”式参赛选手，“外卡”参赛，“外卡”选手(指没有正常参赛资格而参赛); 通配符

牛津词典

noun

（由持牌人自由决定牌值的）百搭派，变牌
a card that has no value of its own and takes the value of any card that the player chooses
“百搭”式参赛，“百搭”式参赛选手，“外卡”参赛，“外卡”选手（指没有正常参赛资格而参赛）
an opportunity for sb to play in a competition when they have not qualified in the usual way; a player who enters a competition in this way
通配符
a symbol that has no meaning of its own and can represent any letter or number
难以预测的人（或事物）；未知因素；未知数
a person or thing whose behaviour or effect is difficult to predict

N-COUNT 未知数;未知因素
If you refer to someone or something as awild cardin a particular situation, you mean that they cause uncertainty because you do not know how they will behave.
1. The wild card in the picture is Eastern Europe.
  整个局势中的变数是东欧。
N-COUNT （给予没有正常参赛资格的选手准其参加比赛的）“外卡”;“外卡”选手
If a sports player is given awild cardfor a particular competition, they are allowed to play in it, although they have not qualified for it in the usual way. You can also usewild cardto refer to a player who enters a competition in this way.
1. Andre Agassi accepted a wild card to play in the Stockholm Open.
  安德烈·阿加西持外卡参加了斯德哥尔摩公开赛。
(用于代替任何字符或字符串的)通配符
Awildcardis a symbol such as * or ? which is used in some computing commands or searches in order to represent any character or range of characters.

noun