What is a Meaty?
Meaty refers to when an attack hits an opponent during the frames in which they are getting up off of the ground after being knocked down.
Meaty is a spectrum because many attacks have more than one active frame and the later in those active frames a move hits, the "meatier" it is. The more meaty a move is the greater the frame advantage is. Meaty can also be used as a noun to refer to any attack that can be described as being meaty. This is where the common terms "meaty hit" or "meaties" come from.
The available meaty options are character specific and depend on how the opponent is knocked down. Different knockdowns give you varying amounts of time to prepare a meaty before the opponent recovers, thus you will need to use different meaties for different situations.
Meaty Effect on Frame Advantage
Meaty 5K (right) versus normal 5K (left). In the meaty version, the defender begins blocking later and recovers later compared to the attacker.
To demonstrate the added frame advantage meaties gain, let's compare a meaty versus a non-meaty attack.
Both attackers start attacking at the same time, but notice the meaty attack hits later. As a result, the meaty attack has more frame advantage than the normal attack (compare when the defender is able to start walking backwards).
Some meaties even allow you to recover in time to block reversals from the opponent too.
Sliding Hitbox Meaty
The above example take advantage of the opponent's invincible wakeup animation to have our attack hit later. This same effect can be done by spacing an attack that moves forward, such as doing Slayer's 2D from further away. Players can also use the momentum gained from running forward for the same effect!
Meaty Attack Timeline
Time difference for a normal attack versus a meaty attack. Notice that the amount of blockstun is the same, the key difference is that the meaty attack hits later. Depending on the specific move, an attack that is - on block can turn into + on block!
Moves to Use/Avoid
Moves that inflict lots of blockstun and have little recovery are the best meaty attacks because this allows you to maximize the amount of frame advantage gained. Having said that, they must still be fast enough to hit as soon as the opponent is vulnerable.
One common meaty is a meaty projectile. Ky players often use Charged Stun Edge on oki because it gives him lots of time to run towards the opponent while the opponent is stuck blocking the projectile.
On the opposite end of the spectrum, moves that enter a forced recovery state on hit/block (such as Sol's Riot Stamp or Ragna's Hell's Fang) are generally bad meaties since they do not gain any additional frame advantage from hitting "late" into the move because the recovery will always be the same.
Degrees of Meatiness
Since timing is such a big part of meaties, players often make a distinction for meaties that hit later into the move's active frames versus those that hit earlier. There's no formal terminology for these degrees, so players often use intensifiers and downtoners (very meaty, slightly meaty, etc.)
First Frame Meaty Attacks
While the typical definition of meaty means to hit with the later active frames of an attack, players often refer to attacks that hit an opponent immediately as they wake up as meaty, regardless of whether or not it was with the later active frames or not. A Safe Jump is a common example of this.