The most common names (none official) is an "emordnilap" or an "anadrome."
Semordnilap is a name coined for a word or phrase that spells a different word or phrase backwards. "semordnilap" is itself "palindromes" spelled backwards. According to author O.V. Michaelsen, it was probably coined by logologist Dmitri A. Borgmann and appeared in Oddities and Curiosities, annotated by Martin Gardner, 1961.
Semordnilaps are also known as anadromes, volvograms, heteropalindromes, semi-palindromes, half-palindromes, reversgrams, mynoretehs, reversible anagrams, or word reversals.
WOW becomes MOM.
NOON
MOW
Something that looks the same upside down has point symmetry.
The word SWIMS, when written in upper case letters, is the longest word in the English language that reads the same both forward and upside-down with no reading difficulty.
SWIMS
pig on these are both words that look different but are still a word upside down.
The word is NOON.
NOON
its radar dont you get it you people are idiots
NOON
That would an ambigram. That is, if your question meant to say "reads as one word one way, and says something else upside-down."
As long as it is in all capitals, the word "SWIMS" can be read upside down.