##Where did algebra come from?
Algebra has a long history. The earliest recorded use of basic algebraic concepts is from ancient Babylon, where people used it for things like land measurement and trade. The word "algebra" itself comes from a book written by the medieval Persian mathematician Muhammad ibn Musa al-Khwarizmi.
Learn more with our [Origins of algebra video](/v/origins-of-algebra).
##Who invented the algebra that we use today?
Lots of people! Modern algebra is the result of centuries of development by many different mathematicians in many different cultures.
##How is algebra used in the real world?
Algebra is used in countless ways! One example is in computer programming, where variables are used to store data and expressions are used to carry out calculations. Algebra is also used in science, engineering, finance, and many other fields.
Learn more with our [Creative algebra at work video](/v/creative-algebra-at-work).
##How do we use variables in algebra?
We use variables in algebra to represent unknown quantities. They help us generalize mathematical relationships and solve equations.
Learn more with our [Why all the letters in algebra video](/v/why-all-the-letters-in-algebra).
##What's the difference between an equation and an expression?
An equation has an equals sign, while an expression does not. For example, $3x+2$ is an expression, while $3x+2=8$ is an equation.
##What does it mean to "evaluate" an expression?
Evaluating an expression means finding its value when we substitute specific numbers in for the variables. For example, if we evaluate $2x+3$ when $x=4$, we get $2(4)+3=11$.
Practice with our [Evaluating expressions with one variable exercise](/e/evaluating_expressions_1).
##What are "like terms"?
Like terms are terms that have the same variable raised to the same power. For example, $3x$ and $2x$ are like terms because they both have $x$ as the variable, while $3x$ and $2y$ are not like terms because the variables are different.
Practice with our [Combining like terms with negative coefficients exercise](/e/combining_like_terms_1).