Here's the breakdown:

* Main sequence stars are a specific type of star, characterized by fusing hydrogen into helium in their core. They represent the longest and most stable stage in the life of most stars.

* Stars is a broader term, encompassing all celestial objects that emit light and heat due to nuclear fusion.

So, all main sequence stars are stars, but not all stars are main sequence stars.

Think of it like this:

* Stars are like the category "animals".

* Main sequence stars are like the subcategory "mammals".

All mammals are animals, but not all animals are mammals.