ELI5: Explain Like I'm 5

Algebraic number

Algebraic numbers are special kinds of numbers that can be expressed as solutions to equations with whole numbers, called variables. For example, the number 7 can be expressed mathematically as 2x+1=7. We can solve this equation to work out that x=3. So, algebraic numbers are the values of the variables in these equations (like 3 in this example).