Valid / Convalidated Marriage

Someone said their marriage was recently convalidated. What does that mean?

Convalidation (with validation) of a marriage is typically done when a couple, in which at least one of the parties was Catholic, had a wedding which was conducted outside of the rules of the Church for a valid marriage. All marriages are to be witnessed by a priest or deacon, or with dispensation for a person designated by the bishop. Thus, a marriage by a Notary Public or non-Catholic minister, (without a proper dispensation) would not be recognized as a valid marriage.
For example: A couple are in the military and about to be transferred. They are planning to get married but the military will not transfer them together because they are not yet married. They do not have the time needed for a proper wedding (typically 6 months). They go to the local magistrate and are married civilly. Since the Church does not recognize the validity of Catholic marriages unless witnessed by a priest/deacon/designated witness, after the transfer the couple goes to the priest or deacon to request the marriage be convalidated. Here they repeat their vows in front of the priest/deacon with two witnesses. In doing such the marriage is then recognized as valid by the Church

I had a friend who is Catholic who was married by a protestant pastor in her husband’s church. Is that a valid marriage?

It depends.
If the couple worked with the local Catholic pastor to obtain from the bishop a Dispensation from church law, to have the protestant pastor designated as the witness for the Church, then yes, it is a valid marriage. If the couple were married without the proper Dispensation, then I suspect the answer would be, no; they might require a Convalidation of their marriage.

In my diocese, most of the weddings I have done are what we call mixed marriages. This means that one of the parties to the marriage is not Catholic. The Catholic party is required by Church law to have the marriage witnessed by a priest or deacon or person designated by the bishop. This typically involves meeting with the Catholic pastor or deacon, to prepare for the marriage and fill out the proper Church documentation. One of those documents would be a request for a dispensation to marry a non-Catholic. If there is a good reason to do so, the couple in a mixed relationship can request that the bishop designate someone other than the priest or deacon to witness the marriage, such as the protestant pastor. With the proper Dispensation, the marriage is valid, from the Catholic perspective, from the moment of the “I do”.