According to USA Today:
The pope raised the idea in an interview with the German newspaper Die Zeit.
He ruled out the prospect of allowing single men who are already priests to marry but was open to the idea of allowing unmarried laymen or men already married to be ordained.
The pope raised the prospect in the context of allowing “viri probati,” Latin for “tested men,” to be ordained in places with a scarcity of priests.
He told the newspaper the lack of Catholic priests was an “enormous problem” for the church.
“We need to think about whether ‘viri probati’ could be a possibility,” he told the German weekly. “If so, we would need to determine what duties they could undertake, for example, in remote communities.”