What's the difference between the two things you described?
To my understanding, the two options you gave are the same: Dark matter is a hypothesized form of matter which does not interact with normal matter or light (i.e. It can't be seen).
Right I'm not questioning the differences between the two. I'm questioning how we know that the unseen stuff out there is regular matter vs Dark matter. Both matter and dark matter can appear dark when not interacting with light or glowing.
According to my knowledge dark matter is identified through its gravitational properties. Matter and dark matter both are gravitational hence my curiosity on why we're identifying this unaccounted gravitational effect as "dark matter" rather than regular matter.
Because you can have dark matter in a hot gas cluster which means it should heat up and be observable by its radiation spectrum. Also note dark matter isn’t black like normal matter in the absence of light. It’s literally transparent because it doesn’t interact with light.
To my understanding, the two options you gave are the same: Dark matter is a hypothesized form of matter which does not interact with normal matter or light (i.e. It can't be seen).