I have noticed that in many synagogues, before davening, the gabbai customarily asks if anybody "has a chiuv". If there is anybody with a chiuv, he is asked to daven from the amud. The people who are considered to "have a chiuv" are aveilim and those observing yahrtzeit for a parent. What exactly does such a person have a chiuv for? I have thought of a couple of possibilities, but neither of them seem to make sense to me.
They have an obligation to pray. To me, this seems like a very unlikely suggestion. Everybody there has an obligation to pray, and I don't know why a mourner would have a greater obligation.
They have an obligation to lead davening. This suggestion is plausible to me, but I still have some doubts. First of all, there might be more than one person with a chiuv. In that case, would it really be the case that everybody who doesn't lead davening is mivatel a chiuv? I have doubts about that because I have seen people who I know to be very pious and knowledgeable who had a chiuv praying in a minyan where someone else with a chiuv was leading the prayer. If this is truly an obligation, I would expect that those people would find another minyan where nobody has a chiuv. Also, why would having a relative pass away cause someone to have an obligation to lead davening?
So what is the obligation that is being referred to when we say that someone "has a chiuv"? If it is not really actually a true obligation, why is it called that?