There are a lot of differences between a hot tub and a spa, even though today, the terms are used interchangeably. A spa is ideally a hot tub with a number of jets and seating facility and it is built in-ground or above-ground, close to a traditional pool. Spas are larger than hot tubs, and these have more seating capacity than hot tubs.
If you want to install an in-ground spa, you will need to work on the installation of the hot tub by digging up and installing the water and electricity fixtures. An in-ground spa is usually built while a pool is getting constructed, but you can also get these designed and made on order. An above-ground spa is easier to install as you do not need to make space in the ground for it. You can place the spa in the location you prefer and hook it up to the water and electricity supply.