An acute angle is one that is smaller than 90 degrees. A 90 degree angle is a "normal" corner, like you find inside most houses and the corners of a piece of paper. Acute angles can also be described as sharp or pointy. An angle larger than 90 degrees is called obtuse.
The diameter of a circle is the measurement across the circle at its widest point. The man in the picture has his arms across the diameter of the cut tree.
This glass of water is half-full (some people would say half-empty). If you took two half-glasses of water and poured them together, you would get a full glass. A half is what you get when you cut something into two equal sized pieces.
An obtuse angle is one that is larger than 90 degrees. A 90 degree angle is a "normal" corner, like you find inside most houses and the corners of a piece of paper. An angle smaller than 90 degrees is called acute.
Two lines are parallel if they are next to each other and are always the same distance apart. There are many parallel lines in buildings. The vertical lines the bricks make in the right side of the picture are parallel.
