Anything in the universe that has mass (barring one exception) is made out of either Matter or Antimatter. These two concepts are the basic foundation for what makes up the entire universe.
For the most part, They act entirely the same. The difference being that they completely oppose each other and will annihilate each other from existence. Think of it like Hot and Cold, North and South.
For example, If I were to place a Matter object within an Antimatter room. That Matter object would be annihilated. If i were to place an Antimatter object within a Matter room. That Antimatter object will be annihilated. If I were to place a Matter object and an Antimatter object next to each other, They would annihilate each other.
If an article mentions Matter It is most likely referring to both Matter and Antimatter