| I | |
| Improper Fraction | Fraction larger than one whole. |
| Inch | Imperial unit for measuring length. |
| Increase | Get larger in size or number. |
| Inequality | Not equal in size, number or value. |
| Infinite, Infinity | Unable to be counted, unlimited. |
| Integer | Any number positive and negative that is not a decimal or fraction. Includes zero. |
| Intersect | To cross over one another. |
| Interval | Distance between two points. |
| Isosceles Triangle | Triangle with two equal sides and two equal angles. |
| Isometric | Having equal dimensions or measurements. |