Greek mathematics is a type of math that was used a long time ago by people who lived in Greece. They did math in a very special way, using a lot of lines and shapes to figure out problems. For example, they liked to use something called a compass and a straight edge to draw circles and lines on paper.
One of the most famous Greek mathematicians was named Euclid. He wrote a book called "The Elements" which had a lot of really cool ideas in it. In fact, his book was so special that it's still used today in schools all over the world! In "The Elements", Euclid talked a lot about shapes and angles, and he showed how you can do math on paper to figure out things like how big a triangle is, or how to measure the distance between two points.
Another famous Greek mathematician was Pythagoras. He had big ideas about numbers and how they work together. One of his most famous ideas is something called the Pythagorean Theorem. This tells us that in a right triangle, the square of the length of the hypotenuse (the longest side) is equal to the sum of the squares of the other two sides.
The Greeks also liked to think about infinity. They thought that even if you kept counting and counting forever, you would never really get to the end of all the numbers. They even had a special symbol for infinity, which looks like a sideways "8".
Overall, Greek mathematics was really important because it helped us to understand a lot of basic ideas that we still use today. Without the Greeks, we might not know as much about shapes, angles, and numbers!