There has been a lot written in about the three true outcome hitter. Baseball-reference gives us the most concise definition:
The Three True Outcomes are a walk, strikeout or home run. They are called this because the three supposedly are the only events that do not involve the defensive team (other than the pitcher and catcher). This ignores outfielders taking away potential homers at the wall, and inside-the-park home runs, and the like; however, over a career those events make up a very small portion of the total.