Banana paste is exactly what it says on the tin. It is paste made of, and tasting like, bananas. It is usually used for flavoring confectioneries, especially as an flavoring for custard, ganache, ice cream, or icing.
It is made by dehydrating and puréeing bananas, and mixing the resulting powder with glucose syrup (e.g., aui and Predilecta brands) or fat (e.g., Banos brand) and concentrated banana juice (and even more sugar and misc. preservatives), after which is it shelf-stable.
Which sounds fairly sane, but then, humans. My first introduction to the existence of a banana paste was a passing reference to banana paste sandwiches. This is a thing; as are banana paste pancakes, banana paste halva, and banana paste grilled cheese sandwiches. In Brazil
banana paste with cheese is a common treat. Can things be worse? Of course. Google also presented me with a patent for a new method of using the entire banana -- including the skin -- for making edible banana paste.
But that's banana paste, The Food Product. Homemade banana paste, what most people might call simply mashed banana, is apparently the preferred term for banana-as-a-remedy. Banana is claimed to be the fruit of choice for topical application, curing everything from dry skin to dry hair to dandruff to wrinkles to pimples to hemorrhoids (for this last, eat the banana, and make a paste out of the banana skin). Food-grade banana paste should not be used for these purposes.