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Naming conventions

Mathematics has many conventions. Below are some of the more common ones. Many of the symbols have other conventional uses, but they may actually represent a constant or a specific function rather than a variable.

• a, b, c, and d (sometimes extended to e and f) usually play similar roles or are made to represent parallel notions in a mathematical context. They often represent constants or coefficients, for example in a polynomial or an equation, which are not completely specified.
• a₀, a₁, a₂, ... play a similar role, when otherwise too many different letters would be needed.
• f and g (sometimes h) commonly denote functions.
• i, j, and k (sometimes l or h) are often used to denote varying integers or indices in an indexed family.
• a_i is often used to denote the i-th term of a sequence.
• l and w are often used to represent the length and width of a figure.
• m and n usually denote integers and usually play similar roles or are made to represent parallel notions in a mathematical context, such a pair of dimensions.
  • n commonly denotes a fixed integer like a count of objects or the degree of an equation.
• p, q, and r usually play similar roles or are made to represent parallel notions in a mathematical context.
  • p and q often denote prime numbers or relatively prime numbers, or, in statistics, probabilities.
• r often denotes a remainder or a modulus.
• r, s, and t usually play similar roles or are made to represent parallel notions in a mathematical context.
• u and v usually play similar roles or are made to represent parallel notions in a mathematical context, such as denoting a vertex (graph theory).
• w, x, y, and z usually play similar roles or are made to represent parallel notions in a mathematical context, such as representing unknowns in an equation.
• x, y and z usually denote the three Cartesian coordinates of a point in Euclidean geometry. By extension, they are used to name the corresponding axes.
  • z typically denotes a complex number, or, in statistics, a normal random variate.
• $\alpha$, $\beta$, $\gamma$, $\theta$ and $\phi$ commonly denote angle measures.
• $\epsilon$ usually represents an arbitrarily small positive number.
  • $\epsilon$ and $\delta$ commonly denote two small positives.
• $\lambda$ is used for eigenvalues.
• $\sigma$ often denotes a sum, or, in statistics, the standard deviation.