Fire ants are a specific sub-species of ant that are known for their red exterior and painful bites. They aren't nearly as common as normal ants, but they are much more dangerous to humans and therefore are considered a more serious pest. They live in colonies, and they normally create their mounds in open outdoor areas where they can feed on plants and seeds. Fire ants will sometimes attack other bugs or small animals in their vicinity and can be deadly to them in some cases. They are also particularly resilient and have even survived severe floods and hurricanes.
There aren't too many species of fire ant around the world - only about 200, as opposed to thousands of species of other types of ants. They are all part of the solenopsis genus and are typically very similar to each other. The species of ants are mostly differentiated by where they live as opposed to their physical characteristics.
The bites of fire ants are very painful. They actually get their name from the sensation that the bite produces, which is a feeling of being burned. Some people with more sensitive skin have very serious reactions to fire ant bites, so they are not something to be taken lightly. These ants are also very dangerous to the animal and plant population. They are far more harmful to animals than they are to humans, and in some cases can make it quite difficult for animals to get food or water without being stung. Since they like to feed off of plants, they can also disrupt the ecosystem that way.
Since fire ants are so resilient, you are going to need some particularly strong preventative methods to keep them away. A common solution is to place baits for the fire ants, but this can take months to be effective. A faster option is to use a liquid mound drench, which you pour onto the top of their colonies. If you don't want to use chemicals, you can also pour a few gallons of hot water into the mound to drown it, making sure to completely saturate the colony. This process will need to be repeated several times to be effective.