A standalone villa is a villa that has boundary walls and stands on its own private land. It is not attached to any other building so it is detached, private and literally "stands alone". Standalone villas are not commonly found in Central Doha including most of the districts within the C-Ring Road as they mainly contain residential and office blocks. However, as you travel further out of Doha and beyond the C-Ring Road it become increasingly common to find standalone villas.
The amenities offered by standalone villas vary depending on the price, size and location. It is much more common to find a standalone villa with a private swimming pool in West Bay Lagoon than it is in Al Khor. Standalone villas are good for large families wanting their own private grounds or for companies looking to accommodate their staff. It is quite common to see standalone villas advertised as suitable for bachelor accommodation. If you are specifically looking for a standalone villa, check the details advertised with the agent as sometimes compound villas are advertised as being standalone when they are in fact not standalone but instead the agent refers to the villa being detached from its neighbouring villa as such.