An "investment" is something that you spend your money on, hoping that you will get more money back in return. Stocks and bonds are common investments. Real estate (houses, buildings, and land) can also be investments.

Tools that you buy in order to do your business can also be called "an investment".

English speakers also sometimes call something that they buy "an investment" when they think that it's going to last a long time and bring a lot of value. For example:

A: How much did that cost?

B: About six hundred dollars.

A: Wow. That's pretty expensive, no?

B: Yeah, but it's an investment. A high-quality jacket like this will last forever.

This use of "investment" is technically incorrect, but it's common.