Other forms: real estates
You don't need to own a fancy estate to own real estate. If you own an apartment, a cabin, or even a little plot of land, you own real estate.
If your grandmother is thinking about buying a condo, she's in the market for real estate, and if your family owns more than one house, they've invested money in real estate. Someone whose job involves helping people buy and sell houses might say, "I work in real estate." This term was first recorded around 1660, but even earlier the word real was used in law for "immovable property."