The infinite jump glitch is when you can jump as high as you want. Here is how. First you use any jetpack (v3 is the best). When the bar loads all the way, keep jumping until there is about one fifth of the bar left. Then quickly click on the little i in the corner. This will pause the game. Then wait a minute or so until you think that the bar on the jetpack would have loaded. Then click ok and quickly press the jump button. The jetpack will use the one fifth of the fuel to keep going, then suddenly the bar will load all the way and you get to keep jumping. Do this over and over until you get as high as you want. I got as high as to, you know, when you look at something really far away, you cant see it because it didnt load? Well I got so high the ground turned the color of the sky. Then I fell down because I was bored. You probably could go infinitely high so use this trick when you get stuck down an astro lair. This photo shows a view looking straight down after the player has jumped up about 150 blocks high:
Looking straight down from a height of about 150 blocks
Above a certain height, probably about 200 blocks above ground level, most of the terrain falls beyond the far end of the OpenGL view frustrum and becomes invisible. Just as you begin to surpass this distance, the view looks something like this:
Looking straight down from a little bit higher, with most terrain rendered "invisible"