"Take-out" is food that you buy from a restaurant, but instead of eating it at the restaurant, you take it home to eat.
In the U.S., the most famous food for take-out is Chinese food. Mexican food, Indian food, and pizza are also popular take-out foods.
Use "take-out" like this:
Why don't we get some take-out?
I don't cook very much. I usually just get take-out or snack on whatever I have in the fridge.
You can also spell this word as "takeout".