[ELI5] What's up with "short sale" houses?

My fiance and I are looking to buy a house this next year (hopefully). We found a realtor whom we love, and we have begin "browsing" the internet for homes. There is one that I've come across that I love however it's a "short sale" The house is a very good house (from what i can tell) and the price is very low. On the mortgage calculator, the mortgage will be almost 1/2 of what our current rent is. We have excellent credit, however we have A LOT of student loan debt that we are working on paying off.

What is a short sale?

Why is a house marked as a short sale? Is something wrong with the home?

Do we still need to get a loan for short sale or do we have to pay for the whole house out of pocket?

Do we still use our realtor to purchase the home?

Any help would be greatly appreciated, as we have no idea what we are doing!

thanks Reddit!