In Algebra, a variable is a symbol or letter of the alphabet that represents a number. This number can be changed and is not fixed, hence why it is called a variable. x is the most common variable used.
eg x + 7 (x is the variable)
eg 2Θ - 7 (Θ is the variable)
In Statistics, a variable is any number or quantity or characteristic that can be measured or counted.
eg Students ages 12, 14, 15, 11, 10, 15, 16, 17, 12, 15
eg Students gender male, male, female, female, male, male, non-binary, male, female
eg Students weekly income $0, $0, $20, $75, $0, $0, $120, $30, $0, $0, $50
eg Students eye colour blue, brown, blue, brown, green, blue, brown, brown