Examples:

edge  The line segment where two faces of a polyhedron, prism, or pyramid meet.

elevation  The height above sea level.

ellipse  A closed, oval, plane figure.  An ellipse is the path of a point that moves so that the sum of its distances from two fixed points is constant.  Each of the fixed points is called a focus of the ellipse.

endpoint  The point at either end of a line segment; also, the point at the end of a ray.  Endpoints, usually labeled with upper-case letters, are used to name line segments; for example, segment TL or segment LT name a line segment between and including points T and L.

equation  A mathematical sentence that states the equality of two expressions.  For example, 2 + 3 = 5 and x + 7 = 6 – 2x.

equator  An imaginary circle around the Earth halfway between the North Pole and the South Pole.  See also latitude.

equidistant marks  Marks equally distant from one to the next.

equilateral polygon  A polygon in which all sides are the same length.

equivalent  Equal in value, but in a different form.  For example, ½, 0.5, and 50% are equivalent.

equivalent equations  Equations that have the same solution.  For example, 2 + x = 4 and 
6 + x = 8 are equivalent equations; each has solution x = 2.

equivalent fractions  Fractions that have different numerators and denominators but name the same number.  For example, ½ and 4/8 are equivalent fractions.

estimate  A “ballpark” answer; a number close to another number; a calculation of a close, rather than exact, answer.

evaluate an algebraic expression  To replace each variable in an algebraic expression with a particular number and then calculate the value of the expression.

evaluate a numerical expression  To carry out the operations in a numerical expression to find the value of the expression.

even number  A whole number such as 2, 4, 6, and so on, that is divisible by 2 (divided by 2 with 0 remainder).  See also odd number.

event  A happening or occurrence.  The tossing of a coin is an event.

expect  To anticipate the outcome of an event or events.  If the red area of a spinner is twice as large as the green area, one would expect red to come up about twice as often as green.

exponent  See exponential notation.

exponential notation  A shorthand way of representing repeated multiplication of the same factor.  For example, 2³ is exponential notation for 2 * 2 * 2.  The small, raised ³, called the exponent, indicates how many times the number 2, called the base, is used as a factor.

expression  A group of mathematical symbols (number, operation signs, variables, grouping symbols) that represents a number (or can represent a number if values are assigned to any variables it contains).

extended fact  See arithmetic fact.