This is the standard for numpad inputs, but many games add or edit the notation. Like how guilty gear has RC(roman cancel). Usually if a fighting game has a wiki there's somewhere that explains it.
Since most different fighting games have different attack types they're represented by different letters. Here's a simple table for the most common. Of course certain games have their own custom button like Quick Attack from MBAACC being represented by E.
| Attack |
Notation |
Tradition 6 Button (Street Fighter, Darkstalker, etc.)
| Light Punch |
LP |
| Medium Punch |
MP |
| Heavy Punch |
HP |
| Light Kick |
LK |
| Medium Kick |
MK |
| Heavy Kick |
HK |
| Attack |
Notation |
Guilty Gear
| Punch |
P |
| Kick |
K |
| Slash |
S |
| Heavy Slash |
HS |
| Dust |
D |
| Attack |
Notation |
Most Anime Fighters (Melty Blood, Unist, etc.)
| A Button |
A |
| B Button |
B |
| C Button |
C |
| D Button |
D |
| Attack |
Notation |
Tekken
| Left Punch |
1 |
| Right Punch |
2 |
| Left Kick |
3 |
| Right Kick |
4 |
When using notation the notation comes before the attack 236S = quater circle slash. Same case with command normal like 6S. Also also like j.S. When written in a combo it'll look like this: S > HS > 236P > 214P > j.K.
That was a acr Ky combo I made up mid match, you might be able to go from 236P > 214D with a RC. It's definitley not optimal though.