For infinite lives, eat one ghost on board 1, 2 ghosts on board 2, 3 ghosts on board 3, and finally 4 on board 4. After you've done this, press Up, Down, Up and die. You'll now have infinite lives.
Otherwise known as the "split-screen level" or a "kill screen", the Map 256 Glitch refers to the 256th level in the original Pac-Man. On this stage, the right side of the screen turns into a jumbled mess of numbers and letters, while the left side is normal.