I will be looking at this from the book/movie standpoint, although it can be applied to real life. In a story, a protagonist try and fight an antagonist. Although he may lose, he gave the reader good entertainment. Additionally, the death may have been necessary for the main protagonist to win in the end. For example, a soldier sacrificing his life for his squad to escape, or Dumbdore deciding he will die so that Voldemort can ultimately lose.
When I think of a glorious defeat I think of the movie 300 or the Alamo. These are situations where the people lost, but they put on such a great fight that their bravery should be remembered for all time. I think that if something is a glorious defeat, it means there were brave men fighting.
I am sure that there is of course a such thing called a glorious defeat or something that is in the same realm of issue when it comes to the topic that is being discussed in our question that is being asked. Some I'm sure can have a type of good defeat.
Anytime, people are fighting for their true rights and come up short is a glorious defeat. They were probably out gunned, and scared out of their minds of what would happen if things do not turn out their way. There is no shame in that. There is no shame in saying that we are not going to let our leaders hold us down, and abuse us, but still coming up short. That is a glorious defeat.
If the defeated person or team went down with a good fight, respect and with class, then yes defeat can be glorious. Most people do not know how to lose graciously, myself included. But I have respect for those who gave all they could and when falling still did it in better ways than those who actually know victory.
I think that there is definitely something like a glorious defeat. I think that there is also something as a tragic winner. I think that sometimes it isn't about winning or losing, but about how one carries themselves while and during such fates. That is why sometimes a glorious defeat is attainable.