Glossary
Plain-English definitions of the concepts behind our tools — each linked to the calculators that use it.
- Amortization
Paying off a loan with equal periodic payments split between interest and principal.
- Annual percentage yield (APY)
The real yearly rate of return once compounding is included.
- Arithmetic mean (average)
The sum of a set of numbers divided by how many there are.
- Base64
An encoding that represents binary data as ASCII text.
- Binary number
A base-2 number system using only the digits 0 and 1.
- Body mass index (BMI)
A weight-to-height ratio used to screen for weight categories.
- Combination
A selection of items where order does not matter.
- Compound interest
Interest earned on both the original principal and the interest already added.
- Confidence interval
A range that likely contains the true value, with a stated confidence level.
- Exponent (power)
The number of times a base is multiplied by itself.
- Factorial
The product of all positive integers up to a given number (n!).
- Greatest common divisor (GCD)
The largest whole number that divides two or more integers exactly.
- Hexadecimal
A base-16 number system using digits 0–9 and letters A–F.
- Least common multiple (LCM)
The smallest positive number that is a multiple of two or more integers.
- Logarithm
The exponent to which a base must be raised to produce a given number.
- Margin of error
The half-width of a confidence interval — how far an estimate may be off.
- Markup
Profit as a percentage of cost (what you paid).
- Median
The middle value of a dataset when the numbers are sorted in order.
- Mode
The value that appears most frequently in a dataset.
- P-value
The probability of data at least as extreme as observed, if the null hypothesis is true.
- Percentage
A number expressed as a fraction of 100.
- Percentile
The value below which a given percentage of the data falls.
- Permutation
An arrangement of items where order matters.
- Prime number
A whole number greater than 1 divisible only by 1 and itself.
- Probability
A number from 0 to 1 measuring how likely an event is to happen.
- Profit margin
Profit as a percentage of revenue (selling price).
- Proportion
An equation stating that two ratios are equal.
- Ratio
A comparison of two quantities showing how many times one contains the other.
- RGB color model
An additive color model mixing red, green, and blue light.
- Scientific notation
Writing numbers as a coefficient times a power of ten.
- Simple interest
Interest charged only on the original principal, not on accrued interest.
- Standard deviation
A measure of how spread out a set of numbers is around their mean.
- Unix timestamp
The number of seconds elapsed since 1 January 1970 UTC.
- Value-added tax (VAT)
A consumption tax collected at each stage of production, shown in the price.
- Variance
The average of the squared differences from the mean.
- Z-score (standard score)
How many standard deviations a value lies above or below the mean.