Mathematics

A is for Acute

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.

Steve Snodgrass / CC BY-SA

A is for Area

Mathematics, Spaces & areas

An area is a part of any surface. Areas are usually separated from everything around them by some kind of boundary, such as a fence or a line drawn around them on a piece of paper.
Area also describes the total size of that area. Different shapes have different formula for calculating how big they are.

Paul Wicks / CC BY-SA

C is for Curve

Mathematics, Shapes

A curve is a line that bends to one side or the other along its length. The opposite of curved is straight.

Peter Kaminski / CC BY-SA

Photo of a man showing diameter on a cut tree

D is for Diameter

Mathematics

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.

Tim Hettler / CC BY-SA

E is for Equal

Mathematics

Two things are equal when there are no difference in the amounts of each thing. For example, two glasses each with equal amounts of wine in them.

L.C. Nøttaasen / CC BY-SA

H is for Half

Mathematics

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.

Roanish / CC BY-SA

Photo of the roofline of a wooden building.

O is for Obtuse

Mathematics

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.

Dan Brady / CC BY-SA

O is for Odd

Adjectives, Mathematics

Something is odd if it is different to usual, or is a bit strange. In a group of things, something that is different is called the odd one out. The man in the picture is wearing odd socks.
Mathematically, a number is odd if it is not a multiple of two.

Chris / CC BY-SA

P is for Parallel

Mathematics, Shapes

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.

seier+seier / CC BY-SA

P is for Path

Mathematics, Paths

A path is a small road that connects two places. Paths are usually for people or animals, not large vehicles.
In math, a path is simply a way to connect two points, not necessarily in a straight line.

John Morgan / CC BY-SA

Q is for Quarter (Fraction)

Mathematics

This apple has been cut into quarters. This means it has been cut into four equal sized pieces.

Lucy Downey / CC BY-SA

Generated image of someone measuring a wheel

R is for Radius (Circle)

Mathematics

Radius is the distance from the center of a circle or a sphere to its edge.

In math and science, radius helps you find other things like the diameter (twice the radius) and the area of a circle.

Photographic Dictionary / Generated Illustration

S is for Scale

Mathematics, Sizes

Scale describes the amount something is smaller or larger something is from its real size, or just a general description of size, like a large scale project.

It is also the singular of scales.

Photographic Dictionary / Generated Illustration

T is for Thirds

Mathematics

This stone has broken into thirds. This means it has been cut into three equal sized pieces.
See also third.

Alan Levine / CC BY-SA