I'm from the Italian region of Puglia, where most masserie are located, so I'm glad to answer your question.
A "masseria" (plural "masserie") is a fortified farmhouse or country house on an estate. The term is most often used in the Italian region of Apulia ("Puglia" in Italian). A masseria is similar to a hacienda in Spain or a plantation in the United States. The masseria was like a rather large farm complex, where the land barons stored their food and possessions from the 16th to 18th centuries in Italy.
The masserie was once the heart of vast land estates, surrounded by rolling fields, groves and pasturelands, inhabited in the summer months by the landowners and the peasant farm workers who tended to crops and the farm animals. The complex usually included several other specialty buildings to house animals, to store crops, or to make wine or cheese. Some masseria developed into essentially small villages surrounded and protected by high walls, with a central courtyard surrounded by all the other structures.
In the 1990s there was a trend to restore the crumbling masserie back to farmhouses and convert them into bed and breakfasts, boutique hotels, rentals or restaurants to accommodate tourists. Masseria lodging range from rustic to luxurious, and most have a swimming pool and garden. Some masserie have a restaurant serving typical dishes of Apulia and a few have cooking classes for guests. Other luxury amenities can include full spa services, golfing, and beach clubs. Most are set in working farms that produce olive oil or wine.
You can read more about masseria on: https://it.wikipedia.org/wiki/Masseria
Examples of masserie for rent: https://www.salentodolcevita.com/en/vacanze-salento?tipo=masseria-fortified-farm
Sorry for the long answer! I hope it helped though!