Examples:

magnitude increase  A 10-fold increase in value.

magnitude estimate  An estimate of the size of a numerical result – whether it is in the tens, hundreds, thousands, and so on.

map direction symbol  A symbol on a map that identifies north, south, east, and west.  Sometimes only north is indicated.

map legend  A diagram that explains the symbols, markings, and colors on a map.  Also called a map key.

map scale  A rate that compares the distance between two locations on a map with the actual distance between them.  The rate is often represented by a labeled line segment, similar to a ruler.

mathematics  A study of relationships among numbers, shapes, and patterns.  Mathematics is used to count and measure things, to discover similarities and differences, to solve problems, and to learn about and organize the world.

maximum  The largest amount; the greatest number in a set of data.

mean  A typical or central value for a set of numbers found by adding the numbers in the set and dividing the sum by the number of numbers.  It is often referred to as the average.

median  The middle value in a set of data when the data are listed in order from smallest to largest (or largest to smallest).  If there is an even number of data, the median is the mean of the two middle values.

memory  Storage of information for later recall.  A calculator’s memory stores a value while other operations are performed.

meridian bar  A device on a globe that shows degrees north and south of the equator.

meter (m)  The basic unit of length in the metric system, equal to 10 decimeters, 100 centimeters, and 1000 millimeters.

metric system of measurement  A measurement system based on the base-10 numeration system and used in most countries in the world.  Units for linear measure (length, distance) include millimeter, centimeter, meter, kilometer; units for mass (weight) include gram and kilogram; units for capacity (amount of liquid or other pourable substance a container can hold) include milliliter and liter.

midpoint  A point halfway between two points.

milliliter (mL)  A metric unit of capacity, equal to 1/1000 of a liter and 1 cubic centimeter.

millimeter (mm)  In the metric system, a unit of length equal to 1/10 of a centimeter and 1/1000 of a meter.

minimum  The smallest amount; the least number in a set of data.

minuend  See subtraction.

mixed number  The sum of a whole number and a fraction.  For example, 2 ¼ is equal to 2 + ¼.

mobile  A sculpture made of rods and other objects that are suspended by strings or wires.  The objects are connected so that the sculpture is balanced and can turn.

Möbius strip or Möbius band  A shape with only one side and one edge; named for mathematician Augustus Ferdinand Möbius.

modal  The adjective form of the word mode.

mode  The value or values that occur most often in a set of data.

multiple of a number n  The product of a whole number and the number n.  For example, the number 2, 4, 6, 8, and 10 are all multiples of 2 because 2 * 1 = 2, 2 * 2 = 4, 2 * 3 = 6, and so on.

multiplication  A mathematical operation used to find the total number of things in several equal groups, or to find a quantity that is a certain number of times as much or as many as another number.  Numbers being multiplied are called factors.  The result of multiplication is called the product.  In 5 * 12 = 60, 5 and 12 are factors.  60 is the product.  Division “undoes” multiplication; 60/5 = 12 and 60/12 = 5.

multiplication fact  See arithmetic fact.

multiplicative inverses  Two numbers whose product is 1.  For example, the multiplicative inverse of 5 is 1/5 and the multiplicative inverse of 3/5 is 5/3, or 1 2/3.  Multiplicative inverses are also called reciprocals of each other.

multiplication property of –1  The property that for any number a, (-1) * a = a * (-1) = (op) a, or –a.  For (op), see opposite of a number.

mystery graph or mystery plot  An unlabeled graph or plot.  The viewer is challenged to figure out a situation it might represent.