The last batch of League of Legends contained phrase the confused a surprising number of people: input buffering. It's not altogether unexpected that the term would be one that is unfamiliar to a MOBA player. The MOBA genre is seen by many as an offshoot of the RTS genre, a comparison the exists mostly due to MOBAs coming about via the custom game mode of Warcraft 3. Input buffering, on the other hand, is a concept that was born in the fighting game genre and simply refers to the ability to input a command while another command is being executed. In fighting games that might help you execute a combo more effectively or, more importantly, cancel an otherwise predictable line of play and pivot into another on the fly.
In League of Legends, the uses are rarely that complicated, however. Typically input buffering is more about getting your commands to execute in quick succession in League than it is anything else, which is why the most recent changes were marketed as changes designed to make the lives of high ping players easier, even if they also completely broke Karthus in Korean solo queue as well. We've already seen this kind of change have an impact in the past, though, as Alistar had a similar change in the recent past that allowed the infamous Headbutt/Pulverize combo to be executed via input buffering, instead of just relying on perfect timing.
Ping-related issues aren't the only application for input buffering in League of Legends, and know it or not you've probably been using it all along, at least if you've been playing some very popular champions properly. Both Rengar and Orianna make extensive use of input buffering, and both have been extremely common picks for some time now.
Orianna actually makes use of the concept in two ways, as both Command: Dissonance and Command: Shockwave react to it in different ways. If you cast Dissonance while the Ball is on the move, it will execute once the ball reaches its destination. That's an example of input buffering at it's finest. Shockwave works differently in that you're allowed to execute it during the movement animation of the Ball, but it will complete during said animation as well if you go about it wrong, whereas Dissonance always goes off at the target location. Usually, they work out to having the same function, but not always, and any skilled Orianna has undershot their ult just as many times as they've made the infamous "sombrero" play.
Rengar's case is much more straightforward but is also absolutely essential to using his kit properly. If you cast savagery while Rengar is leaping around with his passive, it will immediately execute the moment he lands on his target, which is something that you effectively always do while playing Rengar as it enables him to get to an empowered cast as quickly as possible. if you haven't been doing that before now, start doing it today!
So, as you can see, as intimidating of a concept as input buffering might seem at first glance, it's really nothing all that difficult to understand. It's appilcations are numerous and certainly not limited to the examples listed here. In fact, most champions can make use of input buffering in one way or another, though it may not be required the same way it is for the example we listed here. Get the hang of executing your commands in quick succession, and it will be all the easier to take the opposition by surprise and win some of that sweet, sweet LP.