"Meta" is a prefix indicating something going one way, then back to itself. For example: a story about a story. "Trans" in this case refers to gender identity and gender expression, see transgender
Meta trans could be the definition of your state when you have one biological sex, identify as the other, but express yourself in a way that is more common among the opposite to what you identify with. Another less formal term for it could be trans-ception (from the term ‘inception’ which people informally use to describe something "mindfuck
When you feel like there's no link between your (e.g. female) body and your preferred (e.g. feminine) expression (since the gender expressions are socially constructed) – you can still identify as male or something between or beyond male and female.
I coined this term because this is the way I feel sometimes, and I know many other people who do. With that I want to show that there's a huge variation among people within the transgender spectrum, and not just typically feminine transwomen and masculine transmen.
These are people who could define themselves as meta trans:
An effeminate transguy (FtM)
A transgirl (MtF) who is also a tomboy