In mathematics when an equation is exactly in balance we say that both sides are equal. We show this relationship with an equal sign.
When the two sides of the equation are not equal then one of the sides has to be larger. When the left side is larger than the equation reads "The left side is greater than the right side." and we use a greater than sign. When the right side is larger than the equation reads "The left side is less than the right side." and we use a less than sign.
Sometimes we want to include the number on the right side and still establish an inclusive relationship between the left and right sides. In this case we use the relationships greater than or equal to and less than or equal to. These relationships are also important because they are the inverse relationships for the greater than and less than relationships. The inverse of greater than is less than or equal to, not just less than. Similarly the inverse of less than is greater than or equal to not just greater than.