A characteristic or phenomenon which,is capable of being measured and changes its value from time to time, place to place or situation to situation is called a variable. In other words, anything which is subject to change in value and can be measured is called a variable. Variable means "which varies". It may vary over time, person to person, place to place etc. for example, Income is a variable as it varies person to person (different people earn different incomes), place to place (salaries vary in India and America) and over time (salaries in 1951 were different from salaries in 2001). Temperature is a variable. It changes over time and also place to place. Height is a variable as it varies person to person and over time.
There are two types of Variable:
Discrete and Continuous
Discrete Variable: A discrete variable is one which increases in jumps or in complete numbers. For example, there can't be 2.4 workers in a factory. They can be 1, 2, 3, 4 and so on. Similarly, a factory can't have 4.8 or 2/7 machines. It will be in complete numbers like 1,2,3,4, and soon. Such variable are called discrete variable. Some other examples of discrete variable are number of workers in a factory, number of machines purchased, number of children etc.
Continuous Variable: Those variables which can assume any value in a given range and which increase continuously and not in jumps are called continuous variable. For example, weight of a person can be 45.234 kg, it can take any value within a range. No one gains weight in jumps. It increases in continuity. Other examples are height, income etc.