The delta meaning depends on where you meet the word: delta is the fourth letter of the Greek alphabet (written Δ or δ), and from that letter come its other main senses, a triangle-shaped area of land where a river splits and meets the sea, and a symbol for change in math, science and finance.
Ask three people to define delta and you may get three answers. A geography teacher, a physics student and a stock trader can each say the word and mean something different. This page sorts out each delta definition, gives clear examples, and explains how a single letter came to name a landform and a change.
Entry at a glance
Meaning
Greek letter Δ; river delta; a change or differencePart of speech
Noun (plural deltas)Pronunciation
DEL-tuhSymbols
Capital Δ, small δOrigin
Greek delta, from Phoenician daleth, a tent door; letter name in English from about 1200, river sense from the 1550sRelated forms
deltaic (of a river delta), deltoid (triangle-shaped, as in the shoulder muscle)Register
Neutral; technical in math, science and finance
Delta meaning: the main senses
- A Greek letter. Delta is the fourth letter of the Greek alphabet, matching our D. Capital Δ is a triangle; small δ looks like a curled d.
- A river delta. Low, flat land at a river's mouth, built from mud and sand the river drops as it slows and splits into channels before reaching the sea.
- Change or difference. In math and science, Δ before a quantity means the change in it: Δt is a change in time. In business talk, the delta is simply the gap between two figures.
- Option delta (finance). How much an option's price is expected to move when the price of the asset it is based on moves by one unit.
- The letter D in radio spelling. In the international spelling alphabet used by pilots and soldiers, D is said as Delta.
Delta in sentences
- The Ganges and Brahmaputra form one of the largest river deltas on Earth, home to the Sundarbans mangrove forest.
- In the formula, Δv stands for the change in velocity.
- The delta between our forecast and actual sales was almost ten percent.
- Rice grows well in the delta because the soil is rich and the land is flat and wet.
- The pilot spelled out the call sign: Bravo, Delta, Seven.
How a river delta forms
A river carries tiny bits of rock, sand and soil, called sediment. When it reaches calm water such as a sea or lake, it slows down and can no longer carry its load. The sediment settles, building up new land. Over time the river splits into smaller channels, called distributaries, that spread across the new land in a fan or triangle shape.
Deltas are often very fertile, so many have been farmed and settled for thousands of years. They are also low-lying, which makes them sensitive to floods, storms and rising sea levels. Famous examples include the Nile delta in Egypt, the Mississippi delta in the US and the Ganges and Brahmaputra delta shared by India and Bangladesh. Delta land supports rich biodiversity, from mangroves to wading birds.
Origin of the word
The Greek letter delta came from the Phoenician letter daleth, which is usually said to mean door, likely a tent door. English has used delta as the letter name since about 1200. The geography sense goes back to the ancient Greek historian Herodotus, who noticed that the land at the mouth of the Nile looked like a capital Δ. English borrowed that use in the 1550s, and before 1800 it had spread to any river mouth of this kind, whatever its exact shape.
Using Δ for change grew from mathematics, where the letter became the standard sign for a difference between two values.
Delta definition in finance
Traders use delta to describe how sensitive an option is to price moves. A call option with a delta of 0.6 is expected to gain about 0.6 units of value when the underlying share rises by 1 unit. Call deltas range from 0 to 1, and put deltas from 0 to minus 1. A delta near 1 means the option moves almost one-for-one with the share; a delta near 0 means it barely reacts. Delta also changes as prices and time change, which traders track with another measure called gamma.
Other uses and look-alikes
| Term | Meaning |
|---|---|
| Delta wing | A triangle-shaped aircraft wing |
| Deltoid | The triangle-shaped muscle on top of the shoulder |
| Small δ | A very small change, or a partial charge in chemistry |
| Delta variant | A strain of the virus behind COVID-19, one of several named with Greek letters |
| Delta sleep | Deep, slow-wave sleep shown by delta brain waves |
In everyday office talk, people may ask what is the delta? meaning what has changed or how big the difference is. It sounds technical, so with a general audience, difference or change is clearer. Related science words such as entropy and density fill the science and ideas hub.
Frequently asked questions
Why is a river delta called a delta?
Because the land at the mouth of the Nile looked like the Greek capital letter Δ, a triangle. The ancient Greeks gave it that name, and it spread to other river mouths.
What does delta mean in math?
The capital Δ means the change in a quantity, usually the final value minus the starting value. For example, Δx is the change in x.
What is the definition of delta in simple words?
Delta is a Greek letter. People also use it to mean a change or difference, and to name the fan of land where a river meets the sea.
What does delta mean in business?
In meetings it often means the difference between two numbers or plans, such as the gap between budget and actual cost. It is informal jargon for change or gap.
What is the plural of delta?
The plural is deltas, as in the great river deltas of Asia. The adjective for river deltas is deltaic.
How do you write delta?
The capital form is Δ, a triangle, and the small form is δ. In English text you can also just write the word delta.