In FF7 the same memory address is used by the game to take you from one field to another as well as take you from a field to a battle and then back to the field again.
Normally these two events (field changes and battles) run smoothly and don't conflict each other, but thanks to a certain relatively minor glitch we can make these to events conflict and as a result provoke one major glitch.
If you open the menu on the same frame as you get a random battle (not on the world map) the battle will be canceled.
If you exit a field at the very same frame as you get into a random encounter you'll normally first fight the battle and then get transferred to the new field.
But if you use the Menu-glitch the battle will be canceled and the game will instead use the Battled ID to decide what field you'll get transferred to!
While the Glitch might seem very powerful at first glance it is in fact, due to how it works, very limited. You can only warp from Fields with enemies, and only warp to Fields dictated by the Battle IDs.
The vast majority of fields you can warp to will just have Cloud stuck in a wall, and many of the few fields where you won't spawn in a wall will instead present other obstructive glitches later on.
Skip Tifa's bar in the Sector 7 Slum and you'll be without the Materia menu. Skip the end of Kalm and you'll be without the PHS. And the list of possibly problematic circumstances goes on.
But even if most warps will be of no use there are still many that can be used and abused, setting new standards for Speed Runs and Perfect Games.