You may have heard other players use the terms "inside" and "outside" english. To help you understand these billiard terms, I will try to explain them with a couple of illustrations.

Figure 1

Figure 2

This terms are a little confusing at first but once you get the idea, it should be simple enough. Let's start with "inside" english. Refer to the first illustration on the left. Here you are shooting the object ball to go to the left (from the shooter's point of view) into the corner pocket. If you apply left english on your cue ball, this is called "inside" english. If you apply right english on the cue ball, this is called "outside" english.

Still confused? Let's look at the next illustration. Here you are shooting the object ball to the right (again, this is from the shooter's perspective) into the corner pocket. Applying right english on the cue ball is called "inside" english while applying "left" english is called "outside" english. So, what have we learned? To summarize, if the direction of your english is the same as the direction of the object ball into the pocket, you are using "inside" english. If the direction of your english is opposite that of the direction of the object ball into the pocket, you are using "outside" english.

Another way to understand inside and outside english is to look at the angles. Refer to the first illustration on the left. If you use left english on the cue ball, you are on the "inside" or smaller angle. If you use right english, you are on the "outside" or the bigger angle.