What is what the sigma?

Sigma (σ, Σ) is a letter in the Greek alphabet. However, in various contexts, especially in mathematics, statistics, and engineering, it represents specific concepts. Here's a breakdown:

• Summation (Σ): This is perhaps the most common usage. The capital sigma (Σ) denotes the sum of a series of terms. For example, Σ(i=1 to n) xi represents the sum of the values x1, x2, ..., xn. Learn more about Summation.

• Standard Deviation (σ): In statistics, the lowercase sigma (σ) usually represents the standard deviation of a population. It measures the spread or dispersion of a set of data from its mean. Check out Standard%20Deviation.

• Variance (σ²): The square of the standard deviation (σ²) represents the variance. Variance is another measure of data dispersion. Explore Variance.

• Sigma Bonds (σ): In chemistry, sigma bonds are the strongest type of covalent chemical bond. They are formed by head-on overlapping between atomic orbitals. Read about Sigma%20Bonds.

• Electrical Conductivity (σ): In physics, lowercase sigma (σ) can represent electrical conductivity, which is a measure of a material's ability to conduct electric current. Look into Electrical%20Conductivity.

• Stress (σ): In materials science and engineering, sigma can represent stress, which is the force acting on a cross-sectional area of a material. Read more about Stress.