Okay kiddo, so you know how when important people like popes and bishops pass away or resign, they need to choose a new leader? Well, this special meeting where they pick a new leader is called a "conclave."
Sometimes, there might be a situation where none of the leaders being considered have enough support to become the new leader. When this happens, they might try to come to an agreement. This is called a "capitulation."
So, a "conclave capitulation" is when the people choosing the new leader of a church or religious group can't decide on someone and they all agree to choose someone else who wasn't being considered before. It's like saying, "Okay, we couldn't decide on any of these guys, so let's choose Bob instead!"
It's not the preferred way of choosing a leader, but it can happen when there are disagreements and no clear choice emerges.