Reversals: A reversal creates a brief window where you cannot block some attack types, but will automatically stop others. Some reversals like Asuka's take the form of inescapable throws when successful. Others, like Law's, cause a stun and allow the reverser to get a free hit. The most common reversal is a short-lived punch reversal for mids and highs. Steve, Paul, Hwoarang and others have this.
Reversals can commonly be punished on reaction if whiffed. Many can be chickened. Most reversals cannot reverse knees, elbows, shoulders or headbutts.
Unique reversals include Asuka's and Geese's.
Sabakis
A sabaki is an attack that's simultaneously a reversal. Instead of being counterhit by a particular kind of attack, you'll reverse it. Worth noting is that the reversal frames usually do not last throughout the entire sabaki attack. For example, a 23 frame punch sabaki may have only have reversal properties for its first 6 frames! Any attack, including punches, will counterhit it as normal outside these frames. Sabakis cannot be chickened.
Parries
Parry is often used interchangeably with reversal, but these are distinct types of move. Similar to a reversal, a parry may catch specific kinds of attack. But where a reversal stops the attacker dead, a parry simply makes the attack whiff. Normally, a successful parry triggers an automatic move that prevents the attacker ploughing on. But since it doesn't stop strings or freeze the attacker, this is chancier than a reversal.
Parties typically can't be chickened. Some examples of parries are Jin's parry, Yoshimitsu's Kincho stance startup, and Master Raven's Utsusemi Escape. Like reversals, these are often whiff punishable on reaction.