Cardinal electors are the Cardinals of the Catholic Church who are eligible to enter the conclave and will cast ballots to elect a new pope. Of the 207 total cardinals in the Church 117 cardinals qualify as “Cardinal Electors.”*
According to the Vatican Information Service blog:
John Paul II’s Apostolic Constitution “Universi Dominici Gregis”, which will regulate the conclave, establishes in no. 33 that cardinals who have reached their eightieth birthday before the day when the Apostolic See becomes vacant will not be cardinal electors. For that reason, for example, Cardinal Walter Kasper, who turns 80 on 5 March will be an elector, as is also the case for Cardinal Severino Poletto, who turns 80 on 18 March.