Attack properties

In Tekken attacks can have one of the following properties:

High
High attacks are blocked standing, however while crouching the attack will whiff. Most High attack are safe on block and have good Tracking. 

Mid
Mid attacks are blocked by standing but hit crouching opponents. Usually Launchers and important moves are mid, for example d/f 1. 

Special Mid
Special Mid attacks are moves that can be blocked both by standing and crouching. Special Mids are pretty rare, the most important Special mid is the low Jabs. 

Low
Low attacks must be blocked crouching and hit standing opponents. Lows are very commonly used to open up the opponents defense, but are generally unsafe. Low Pokes tend to be punishable around 11-14 frames. Lows that Knock-down or launch are -15 or more, thus being launch punishable by the majority of the cast. 