**Algebra** is a universal mathematical language, so it uses specific vocabulary to help us communicate different ideas.

Here are some of the key words we use in algebra:

**Term** is part of an expression. It consists of letters and/or numbers.

**Variable** is a part of a term and is represented by letters, usually *x*, or symbols. Variables can take any value.

**Coefficient** is the number that stands in front of the variable.

Let's see these in action now.

**e.g. 10 x**

The** term** is 10*x** *as a whole, the **coefficient **is 10 and the **variable **is *x*.

**Expressions** are made up of algebraic terms which are connected by mathematical operator (+ , -, x, /).

They** do not** include an equals sign.

Here's an example of an **expression** with three **terms**: 3*x*^{2} - 4*x* + 5

The** terms **are: 3*x*^{2}, 4*x, *5

3x2−4y+2

**Equations** are the same as expression but they **do **contain an equals sign.

As a result of this, we can solve them for **some**, but not all, values of *x* (or another variable).

This is an** equation**: 5*x* + 9 = 24

And so is this: *x*^{2} + 3*x* - 12 = 0

**Formula** is related to an equation.

Formulae will also have an **equals sign**, but they will be true for **many** values of the variable.

Therefore, we cannot solve a formula, unless we know the values of some of the **variables**.

You might have seen some formulae in maths or science already.

Some well-known examples include:

Formula for speed:** s = d ÷ t**

Formula for area of a circle:** A = πr ^{2}**

To use these formulae, you need to know the value of one (or more of the variables).

In this activity, we will identify where these definitions apply and, therefore, which calculations we can and cannot perform in each situation.