To represent means to be used in place of another value. So for instance, if you have x + 10 equals 20, then x represents a number, which you would now be required to calculate.
The term represent has been used in other fields like biology, finance and so on. And it basically means the same thing as it does in algebra, that is, to be used in place of something else (another value).
Take finance for example, you may be told that a certain equation or function represents the profit of an organization. This simply means, rather than being given the figures which would be profit, you would be given an equation or function which you would apply in place of the profit itself.