An IMNCE is an In Mission Noclip Exploit (sorry I didn't know exactly what to call it, if you come up with a better name for it then I will consider changing it to that)
It involves the use of spamming F1 while in mission to go through walls or to fly (repeatedly hitting noclip allows the player to move in any direction (if done right) without the player worrying about gravity or wall collisions)
it doesn't involve using noclip normally or the use of caser noclip exploits
The reason why there is a category for it is because I believe it takes away a lot of interesting strategies that require more skill to pull off. ( it can replace almost all prop climbing giltches, deck clipping giltches and prop rotation giltches with the added bonus of being easier to pull off ( you just spam F1 really fast)).
hope this answers your question