Hero
Hero is the name for the player whose point of view is used in a hand discussion. The hero is you or the player you are following, and the opponent is the villain.
The simple explanation
When people post a hand history or tell a story, they describe the decisions of the hero: 'Hero raises with ace-king and the villain calls.' It is a convenient way to keep the point of view clear, without naming players.
A closer look
The hero and villain convention was popularized by internet forums. The hero's cards are known, and the villain's are not, until the end. Good analysts specify positions, stacks and reads for both players. Some writers dislike the words and use player names or positions instead, such as 'the hijack' or 'the big blind'. The labels do not mean anything about who is right: a hero can make a bad play.
A practical example
A forum post says: 'Hero has ace-king on the button, villain is a tight player in the small blind.'
Full explanation
Hero is the name for the player whose point of view is used in a hand discussion. The hero is you or the player you are following, and the opponent is the villain.
Hero is the player from whose perspective a hand is described. The other player is the villain.
The words make a hand history easier to read, because everyone knows whose decisions are being analyzed.
The hero is often the person who posts the hand and asks for advice.
Being the hero does not mean being right: the question is usually whether the hero played correctly.