Short Answer:
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.”*
Details:
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.
On the other hand Cardinal Husar of the Ukraine will turn 80 on February 26, 2013, and will thus become ineligible (by two days) to be a Cardinal Elector for the upcoming conclave.
While cardinals who are over the age of 80 cannot be electors they can still participate in the pre-conclave meetings and discussions. They can also be selected to be the next pope.
*Although 117 cardinals are qualified to be electors, it appears that there may be 115 cardinal electors in attendance for the 2013 conclave. Cardinal Julius Riyadi Darmaatmadja, Archbishop Emeritus of Jakarta has announced that he will not be attending the conclave due to severe health problems with his eyes. And in the UK, Cardinal Keith O’Brien will not travel to Rome for the conclave following Vatican acceptance his resignation as Archbishop of St. Andrews and Edinburgh. O’Brien, who is embroiled in allegations of inappropriate conduct, stated he would not attend the upcoming conclave at the Vatican as he did not “wish media attention in Rome to be focused on me.”
