The protagonist is generally considered the main character in a narrative, around whom the story revolves. This character often faces challenges, undergoes some form of growth, and drives the plot forward. They typically represent the central theme or conflict of the story and are someone the audience is meant to empathize with or root for.
In contrast to supporting characters or antagonists (who are typically in opposition to the protagonist), the protagonist's actions, decisions, and journey are what shape the overall narrative.
For example, in "Harry Potter and the Sorcerer's Stone" by J.K. Rowling, Harry Potter is the protagonist. The story is primarily told from his perspective, and his struggles against Voldemort (the antagonist) and his growth as a wizard form the heart of the narrative.
So, the correct understanding is that the protagonist is indeed the main character, and this is why identifying them as anything other than that would be incorrect.