Launch Angle
The vertical angle the ball leaves the bat.
What it actually is. Launch angle: the vertical angle the ball leaves the bat, in degrees. Zero is a line parallel to the ground and negative numbers are hit into it.
What a scout reads off it. Angle without speed is a can of corn. The two only mean anything together, which is the reason barrel rate exists rather than a leaderboard of either one.
Where the lines are. Roughly 25 to 30 degrees is home run territory when the ball is hit hard enough. Ten to 25 is line drive country and the highest-average zone in the game.
Batter's Eye: look up anything in baseball