1 Lucas: Okay. We climb up the old fashioned way, then. Give me a boost.
2 Dustin: Wait. This is a D&D adventure. If any of us have thief skills, we can climb walls!
3 {beat}
4 Dustin: Well?
4 Lucas: Let me test by stabbing you in the back.

Early editions of Dungeons & Dragons included a special ability for player characters of the thief class, called backstabbing. This was defined as the ability to cause additional damage when striking an unaware opponent in close quarters from behind. So thieves would often attempt to sneak around behind guards and apply this initial blow before an all-in combat began.

The 5th edition of D&D has changed this to a "sneak attack", which works very differently mechanically. You no longer have to attack from behind, and the opponent doesn't need to be unaware, and in fact you can also apply it to a missile weapon attack. You can apply the sneak attack effect if you have advantage on your attack for any reason, or if you have an ally within 5 feet of your target (presumably distracting them).

In fact the sneak attack is so different that it took me some time to find anything even roughly equivalent to the old backstab attack effect when flipping through the 5e Player's Handbook just now.