# sigma

/ˈsɪɡmə/ (US) · /sˈɪɡmɐ/ (UK)

Source: https://englishreference.com/word/sigma
Updated: 2026-08-15

## Senses

### 1. Greek letter

noun · CEFR C1 · Academic

the eighteenth letter of the Greek alphabet.

For teachers: the eighteenth letter of the Greek alphabet (upper case Σ, lower case σ or ς).

- The professor wrote the Greek letter sigma on the board to start the lesson.
- The student struggled to distinguish between the initial and terminal forms of the lowercase sigma when transcribing the ancient manuscript.

### 2. summation symbol

noun · CEFR B2 · Technical

a symbol used in math to show that you should add a group of numbers together.

For teachers: the uppercase Greek letter Σ used as an operator to denote the summation of a sequence or set.

- You use the sigma symbol to find the total sum of all the scores.
- The formula requires the use of capital sigma to represent the summation of all variables within the defined range.

### 3. standard deviation

noun · CEFR C1 · Technical

a symbol used in statistics to show how much numbers vary from the average.

For teachers: the lowercase Greek letter σ used to represent one standard deviation from the mean in a probability distribution.

- In this chart, one sigma represents the typical spread of the data.
- The quality control team aimed for a six-sigma process to ensure that defects remained statistically negligible.

### 4. independent person

noun · CEFR B2 · Slang · Informal

a popular slang term for a person who is successful and cool but prefers to be alone rather than follow a group.

For teachers: a person, typically male, who is perceived as successful, independent, and self-reliant, existing outside traditional social hierarchies.

- He doesn't care about being popular; he's a total sigma.
- The meme culture surrounding the 'sigma' archetype often parodies the idea of the hyper-focused, solitary achiever.

Teaching tip: This sense is very common in modern internet culture and memes; it is often used with a light quip or a sense of irony.

### 5. cool or independent

adjective · CEFR B2 · Slang · Informal

describing someone who is very cool, successful, or independent.

For teachers: possessing the qualities of a 'sigma' individual; used to describe actions or people that show independence and high status.

- That was a very sigma move to finish the project all by yourself.
- The comments section was filled with users calling the athlete's stoic reaction 'pure sigma'.

## Examples

- The sigma symbol represents the sum of all the numbers.
- In the final report, the researcher used the lower-case sigma to indicate the standard deviation of the test results.
- The Greek letter sigma is ubiquitous in technical literature, appearing as a summation operator in calculus and as a measure of volatility in financial risk assessment models.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.