I can give you another definition for acute angle so an acute angle has a measure or it's smaller than a right angle so you learn about radients and degrees which are different ways to measure angles so you'll see that a right angle can be measured as 90 degrees this over here is less than 90 degrees so this is less than 90 degrees. and one way to conceptualize this is that this angle, it's opening is smaller it's more narrow, it's lines are, you would have to rotate one line