The idea of transformation really comes down to two big questions: Has the material you took from the original work been transformed by adding new expression or meaning? And was value added to the original work in the form of new insight or meaning? To put it more simply: Have you done something other than republish or repackage the original work? If you’ve added new insight or meaning to an original work, you’re probably in the clear.
What may not be fair use, however, is sharing a meme someone else created. First, it depends on how you are sharing. Are you using the share feature on a social media platform like a "reblog" or "share" button, or are you downloading and uploading the meme to your own profile/page/site? The latter would be seen as distributing a copy or making a copy of the content, which would not weigh in favor of fair use.
