What does a line over a letter mean in math?

Let's look into different possibilities of a line over a letter

Answer: The line over a letter in math could represent any of these: complement, bar, or vinculum.

Let's look into the examples of each of these.

Explanation:

Complement: When the line above the letter represents the complement

If x is a set, then the complement of x (denoted by x with a line above it) is the set of all things not in x

It is represented as x̅ 

Bar or Vinculum: When the line above the letter represents a bar.

A vinculum is a horizontal line used in the mathematical notation for a specific purpose to indicate that the letter or expression is grouped together.

The x bar symbol is used in statistics to represent the sample mean of a distribution.

It is represented as x̅ 

Thus, the line over a letter in math could represent any of these: complement, bar, or vinculum.