The sun is much brighter than the star.
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What does the star mean here? Does "the star" refer to all stars or one star which the speaker want to mention?
It refers only to one particular star, but that star is not named.
If you want it to refer to all other stars, then the last word in the sentence should read "... the other stars."
In the phrase "The sun is much brighter than the star," the term "the star" is referring to a specific star that is being compared to the sun. It is not referring to all stars in general.
To determine whether "the star" refers to all stars or a specific star, we can look at the context of the statement. If the statement is made in a general context without any specific star mentioned earlier, then "the star" would likely refer to all stars. However, if there is a specific star being compared to the sun, then "the star" would refer to that particular star.
Without further information or context, it is not possible to determine the exact star being referred to in the statement. It could be any star that the speaker is comparing to the sun.