Commonly used across all fighting games and first introduced in the Dead or Alive fighting game series, the Triangle System is a simple diagram that shows what types of command take priority over each other. According to the diagram, Blocks take priority over Strikes while Strikes take priority over Grabs/Throws. All the while Grabs and Throws take priority over Blocks. Here's a scenario where the Triangle System comes into play:
"You are fighting your friend, Steve and he blocks your mix-up. So you counter with a Grabbing or Throwing attack of any kind (Example: Painwheel's "Buer Reaper", Double's "Godhand", Beowulf's "Wulf Shoot") and therefore according to the Triangle System, your Grab/Throw takes priority over his Block."
However, there are certain moves that involve grabbing that can be blocked, such as the start-up of Valentine's "Dead on Arrival" meaning that such moves count as Strikes, Even though Marie is immune to grab-related attacks. Whether or not a grab-related attack is blockade, therefore counted as a strike depends on various things such as that fighter, the move, etc.