Notation
As the CvS2 wiki is fairly old and contains information from multiple arcade scenes and eras of the FGC, you'll see many different types of notation on here. Modern updates to this wiki will all use Numpad Notation, but older posts and forum posts will usually use Arcade Notation.
Numpad Notation
7 8 9 \ | / 4 - 5 - 6 / | \ 1 2 3
LP MP HP LK MK HK
Numpad Notation is a style of notation invented to be easily readable, easy to type, and universally readable regardless of language. Your character is assumed to be facing right, or on player 1 side. You can read this as 5 being the neutral position of the stick, 6 being forward, and 4 being backward. Numpad notation combines these numbers with the buttons below to notate moves, like for example a crouching light punch becomes 2LP. Motion inputs will combine all of the separate motions, so a quarter circle forward heavy punch would be 236HP. See this guide as well for some more basic motions.
Arcade Notation
UB U UF \ | / B - - - F / | \ DB D DF
Jab Strong Fierce Short Forward Roundhouse
Arcade Notation is the style of notation developed in the days of arcades. Since CvS2 was a major arcade game in its early days, many of the older CvS2 players still use this style of notation, and a majority of old edits and strategy still use it as well. The movement notation is just abbreviated versions of the direction (i.e. UB is up-back, DF is down-forward, etc.). You may also hear directions as simply crouch, jump, towards, away instead. The buttons are based on old arcade cabinets, which would name each button with these names. Jab is a light punch, short is a light kick, roundhouse is a heavy kick, etc. These will be combined similar to Numpad Notation, and sometimes will even use movename abbreviations like it, so a crouching heavy punch would be crouch fierce or c.HP. Special inputs are said literally or abbreviated as well, so you would say quarter circle forward punch or shorten it to qcf+HP.