Definition
A fraction whose denominator is a power of ten (10, 100, 1,000, and so on), written using a decimal point rather than as a numerator over a denominator. For example, 0.25 is a decimal fraction equal to 25/100, and 0.731 equals 731/1,000.
Plain English
A number written with a decimal point that represents a part of a whole, like 0.5 meaning one half or 0.75 meaning three quarters.
Context Anchor
Seen in flight planning, performance calculations, weight-and-balance work, and fuel or time calculations where part of a unit must be written as a number.
Derivation
From the Latin decimus, meaning 'tenth.' A decimal fraction is built on tenths — each digit to the right of the point represents tenths, hundredths, thousandths, and so on.
Why Pilots Care
Almost every number a pilot reads — frequencies, fuel, altimeter settings, weights, distances — is expressed as a decimal fraction. Misreading the decimal place changes the value by a factor of ten, which can matter operationally.
Analogy
Money is a familiar decimal-fraction system: $0.25 means 25 hundredths of a dollar. Aviation calculations often use the same idea, but with units such as hours, gallons, inches, or pounds.
Intuition Check
Do not read the digits after the decimal point as ordinary whole numbers. In 0.75 hour, the 75 means 75 hundredths of an hour, not 75 minutes.
Example Sentence 1
The pilot tuned the radio to 121.5, a decimal fraction representing the emergency frequency.
Example Sentence 2
The latitude coordinate included a decimal fraction for greater precision.