Blend of "header" and "metadata".
Also, happens to be an archaic local variant of a greek letter: ͱ
Heta is the part of a file before the first "empty line".
"Empty line" in this context can mostly be thought of as the character sequence "\n\n".
Note: By implication, Heta can never end with a '\n' character and it can never contain the character sequence "\n\n".
If a file begins with the character "\n", its Heta is empty.
Else, if a file does not contain the character sequence "\n\n", it is all Heta.
ͱdata, or hdata, pronounced "hetadata", is Heta in mdata format.
Also known as "Mdata Heta".