What does it means when a light bulb shattered like explodes by it self without the light been on ?

I went upstairs to use the bathroom I was there for about 2 minutes maybe less
Then I turned off the light switch I walked down stairs I was just half way stairs
and we heard a loud explotion Shattered glass . It was the light bulb. 4 light bulbs
were working at the time . This is the first time in my whole life I experience something like this. The light was off I turned it off.