# Day 4: Flexbox Axes
Flexbox operates in a 2 axes system: a main and a cross axis. The main axis is your defining direction of how your flex items are placed in the flex container. Determining the cross axis is very simple, it's in the direction that's perpendicular to your main axis.
Remember in math class, we were taught x and y axis. Well, throw that out. Because the main axis can be horizontal or vertical. The x axis is not always the main axis. This was a mistake I made, so hopefully you won’t make the same incorrect assumption as I did 😅