Parry Parries are moves in Tekken that let a player deflect opponent's attacking moves during their(parries') active frames and sometimes deal damage to the opponent if parry is succesfull by either automatically playing damaging animation on success or allowing players to perform attacks manually after a succesful parry.
Reversals: Reversal is a special type of a parry which can be chickened. If you can't chicken a parry, then it's just a parry, not a reversal.
Reversals can sometimes be punished on reaction if whiffed.
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.