Soursop, Graviola and Guanabana are all three words for the same plant, the Annona muricata.
In recent years, soursop has gained a reputation as a "Superfruit".
Calling a fruit a "Superfruit" is more or less a marketing term that arose in the food and beverage industry in the last decade. It is generally used to describe fruits that are packed with antioxidants, fiber, vitamins and minerals, and other nutrients.
Graviola was added to the officious list of "Superfruits" both for its nutritious value, but also and quite wrongly, as rumors arose that the soursop fruit can help to cure cancer. This is important to keep in mind, because it is NOT the soursop fruit that is believed to have anti-cancer and other health benefits, but rather other parts of the tree.
However, the graviola fruit IS the most remarkable aspect of the soursop plant. It was first described in the 16th century by the Spanish explorer Oviedo as "...cones, or fruit that resembles them, as large as melons but longish in shape."... 
Not really the most appetizing depiction, if you ask me!
Perhaps my favorite portrayal of the fruit comes from Dr. Christopher Winter, where he describes soursop as "a Granny Smith apple crossed with a pineapple... on steroids" .
The soursop fruit has an absolutely amazing taste, somewhat like mixing banana, pineapple and peaches. I have no idea why on Earth we named it soursop in English. The flavor is neither sour, soppy or sop. My best guess is that the first English speaker to try the fruit liked it so much that he gave it the worst possible name, so as to be able to keep it all to himself.
Due to its taste, the most common use of graviola is as a food source. The fruit, sometimes wrongly referred to as a custard apple in English (which ia actually Annona reticulata or Annona squamosa), is regularly consumed in Jamaica, Latin America and the East Indies, where it enjoys remarkable popularity, and is often found fresh on latin american supermarket shelves or in juice boxes.
Soursop may be eaten in a number of fashions. The least fibrous and least acidic parts of it can be separated from the seeds and consumed directly from the skin with a spoon or cut into small slices. The most common manner of eating it is to squeeze the seeded pulp though a strainer or cheese cloth (or just put the whole thing in a blender), extracting the milky juice which is then combined with water or milk and often sugar to create a smoothy.
Soursop may or may not necessarily be a "Superfruit" in the sense that it gives you super powers or makes you super healthy. However, one thing I can definitely conclude is that the graviola fruit IS super tasty!
About the Graviola Tea Company
The Graviola Tea Company specializes in providing premium quality Annona muricata teas and tea blends to customers around the world.
We regularly receive questions regarding Annona muricata (aka Graviola & Soursop) and maintain this blog in order to answer the most frequently asked questions in an informative and clear manner.
As specialists of Soursop, Graviola & Guanabana teas we believe that we are in a unique position to provide knowledge and insights, and help keep our customers properly informed.
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 Gonzalo Fernández de Oviedo y Valdés. Natural history of the West Indies. Volume 32 of Studies in the Romance languages and literatures. Issue 32 of North Carolina studies in the Romance languages and literatures, NC University of North Carolina Chapel Hill. University of North Carolina Press, 1959.
 Christopher Winter. Is Soursop the Caribbean Secret for Perfect Sleep?. (2013, March 19) [Blog Article]. Available from: http://www.huffingtonpost.com/dr-christopher-winter/soursop-sleep_b_2674521.html