impossible event An event with a probability of 0 .

inch ( in.)  The base unit of length for the U.S. system of measurement.

inequality A sentence with one of the following symbols: <, >, =,  <, >.

infinite decimal A decimal that goes on forever.

infinite repeating decimal A decimal in which a digit or group of digits to the right of the decimal point repeats forever.

instance  An example of a pattern.

integer A number which is a positive whole number, a negative whole number, or zero.

interior angles Angles formed by two lines and a transversal that are between the two lines.

international system of measurement  A system of measurements based on the decimal system. Also called metric system.

interval on a scale The constant difference between successive tick marks on the scale of a graph.

irrational number  A number that cannot be written as a simple fraction. An infinite and nonrepeating decimal.