The feast of the Assumption is when we celebrate the death and "resurrection" of Mary. Eastern Christians focus on her passing (called her "Dormition" - falling asleep), Western Christians also focus on her Assumption (with her body) into heaven. We say Assumption, and not resurrection, to distinguish it from Jesus' resurrection, because there is a sense in which Jesus' resurrection was active - The Father raised him, but he also raised himself, because he is divine. Mary is not divine, so she could not raise herself, so her Assumption is passive - Jesus raised her.

So this means there are no relics of Mary's body, and while there is a site of Mary's tomb in Jerusalem, it has always been empty. It also means that, in addition to Jesus, there is one other person already in the heavenly realm in her resurrection body - Mother Mary. The rest of us (including all the other saints) have to wait until the general resurrection to get our resurrection bodies (i.e., get our bodies back, transformed, redeemed, and glorified).

And in my home, August 15th is also my wife, Tammy's birthday. So we are celebrating both of these things today. And by the way, for Catholics, The Feast of the Assumption is a Holy Day of Obligation, so we go to Mass.

P.S. I call it a "feast" but it's actually a "solemnity" which is a designation for the most important feast days. If I understand it correctly, all solemnities are feasts, but not all feasts are solemnities. It doesn't mean that it's more "solemn" as in serious or sad, it means it's more significant.