Some moves in Killer Instinct put your opponent into a unique state which allows for some special interactions. While not all characters have tools that trigger these states, it's important to understand how they work. Let's take a quick look at them.
Some characters can use moves that are armored. Armored attacks will absorb a single hit without being interrupted, which makes them useful for blowing through certain types of attacks. However, being armored does not protect against throws, and you will still take the damage from the attack the armor absorbed.
Being armored works against all non-throw attacks, with one extremely important caveat; armored attacks lose to grounded heavy normals. This includes all crouching, standing, or command normals that use either heavy punch or heavy kick (but not jumping attacks or specials). If your armor is tied to a resource (like Aganos's chunks), being hit by a grounded heavy normal does not consume your resource, but you will get hit as if your armor was not active, and a special blue hit spark effect will be shown. This allows characters to fight back against armored moves, providing they are willing to press slower, slightly riskier buttons in neutral.
Only a few characters in the cast have access to armored moves. The most notable character in the game is Aganos, who main gameplan involves a resource that keeps him perpetually armored. Other characters that can use armor effectively include Glacius during instinct mode and TJ Combo with his Powerline special move.
If you hit your opponent with any move marked with the wall splat property, you will send them flying backwards a great distance as they reel from the impact. If you use a wall splat move when you are mid-screen, you will simply reset the space between you and your opponent, but if you are near the corner (or one of Aganos's walls), they will collide with the corner and bounce off, and you will be able to continue the combo if your KV meter is not too high.
Importantly, you can throw someone in a wall splat state. This throw does unscaled damage, but can be teched by the defender. There are many strong mixups in Killer Instinct that revolve around whether you will actually perform a throw or try to bait a throw tech after a wall splat, and since the defender is stuck in the wall splat's hit stun, he can not reversal or take any offensive action. They are at the mercy of your mixup.
Many characters have a combo ender that triggers a wall splat; these specific enders are by far the most common way wall splats occur. A select few characters will have normal attacks or special moves that trigger a wall splat outside of a combo, such as Aganos's jumping HK or Rash's Wrecking Ball, but this is very uncommon.
Certain normal or special moves in the game are marked with the stagger property. When you land a move that staggers, your opponent will reel with an exceptionally large amount of hit stun, and you will be free to walk up and continue your combo with any attack of your choice. The best way to classify staggers is to think of them as mid-screen wall splats. You can even throw someone in a stagger state just like a wall splat (and the throw can be teched), although because the KV meter is often very low when you land a stagger move, it is more likely that you will try to continue the combo.
The main difference between wall splats and staggers is that wall splats tend to end combos, while staggers tend to start them. Most moves that cause stagger are strong moves to use in neutral, which means they can form part of the core of your offense and easily confirm into a combo if they hit. In this sense, they are pretty similar to Street Fighter V's crush counters, although stagger does not need a counter hit to activate.
Not everyone has a move that causes stagger. Some example stagger moves include Sabrewulf's and Kan-Ra's standing heavy kick, Arbiter's Plasma Grenade, and Shadow Jago's Dark Reckoning overhead command normal (+HK).
While the previous three states affect grounded opponents, recapture applies to an airborne opponent. When you hit an opponent in the air with an attack that recaptures, they will be brought back to the ground while still in hit stun, which allows you to continue or start a grounded combo. This is important because Killer Instinct's standard combo system only works on grounded opponents. While you can perform juggle combos on airborne opponents, recapturing them allows you to switch from an air combo to a ground combo. This is true whether you hit the opponent into the air with a launching move, or if you simply caught them while they were jumping.
Not all characters have access to a move that recaptures. Even some characters that often use air combos, such as Sadira, do not have a recapture move, which means they must always go for air juggles after they've launched their opponent. Some common recapture moves include TJ Combo's Tremor, Cinder's Crossfire, and Hisako's Shadow Air On Ryo Zan.
While converting an aerial hit into a grounded combo is strong in Killer Instinct, recapture moves when used mid-combo are often easier to combo break on reaction due to obvious strength indicators and longer combo break windows. As a result, recapture needs to be used at unpredictable times, or when mixed in with both long and short juggle combos to keep your opponent uneasy.
Flipout also applies to an airborne opponent. In standard Killer Instinct juggles, the opponent will always land on their back with a soft knockdown when the juggle is over. However, hitting an opponent with a flipout move causes them to flip and land on their feet instead; it is KI's version of the air reset. The character who was hit by the flipout move is invincible until he lands, but the offensive character will usually have plenty of time to apply a mixup on the character as they land from the air.
Like the other states listed on this page, not every character has a flipout move, but a lot of potent rushdown characters will be able to apply this to their wheel of options. For example, after a launcher ender, you might choose to juggle with a sweep for a hard knockdown, or hit with a flipout attack for a fast, surprise mixup; you can combo break both of these attacks, but because they do not share the same strength, reliably breaking them will be difficult. A character like Thunder, on the other hand, might try to use flipout directly after hitting you with his Sammamish special move, creating a scary mixup without needing to use his launcher ender.