In this lesson we're going to talk about some vocabulary that's important to understand. When we get into algebra, we're going to learn about variables and terms. But we'll also talk about constants and coefficients. A variable is a symbol that represents an unknown number. You might remember seeing a problem like this maybe in elementary school. We have five plus some unknown number that was represented by a box or maybe just an underlying space. And then we had to figure out what number was supposed to go in that space. So five plus some unknown number equals eight. And then we could do a little mental math to figure out. Okay, five plus three equals eight and you could figure out how to solve that problem. Well, now that we're getting into algebra, we'll use letters to represent variables instead of boxes or underlined spaces. So that same problem in algebra would be represented as five plus A, or maybe x or some letter, equals eight. But it can be any letter of the alphabet to represent that variable. A term is made of a number of variable or a combination of both numbers and variables together. Now, in expressions, terms are separated by plus or minus signs. So let's look at an example to help us understand. Here's an example of an expression three plus X minus Y. Now notice that we have the three and the X are separated by a plus sign. And then we also have a minus sign that separates the X and the Y. Well, each part of that expression that separated by the plus or minus sign is called a term. So we have three terms here the number three, the variable X, and then also the variable Y. A constant is a term that only includes a number. So in that previous example, that three was just the number. So we could call that a constant. It could be any number, though. So whenever you see a part of an expression that's just a number, no variable with it, then we call that a constant term. A coefficient is a number that is next to a variable in a term. So the number and variable are in the same term together, written right next to each other. There's no plus or minus sign between them. And here's an example, 5a. So when the number is right next to the variable and there's no symbol in between, this tells us that the number is being multiplied by the variable. That's very important to remember. We're used to seeing some type of symbol to represent multiplication. But sometimes in algebra we don't need to use a symbol to show multiplication. We just write the number right next to the variable. So we can say that this represents five times A, but we can just read it as five A. Now the variable in this case is the A and it is being multiplied by the coefficient five. So just remember when a number is right next to the variable, it means they're being multiplied together. So, just to review, a variable is a letter that represents an unknown number. Terms are parts of an expression that are separated by plus or minus signs. A constant is a special type of term that has just a number in it. And a coefficient is a number that is written right next to the variable that shows they're being multiplied together.