What is the term for two kanjis, that when written in the reverse order, have the same meaning? For example, "northeast". I have seen this situation occasionally.
There is no widely-known specific term for this.
There is a website maintained by a Japanese amateur kanji fan, where you can find the list of kanji compounds that makes sense when written in the reverse order (not necessarily the same meaning). The owner of the site calls such words 反対語（はんたいご, literally "opposite word"）. But normally 反対語 means antonyms such as 男/女 and 大きい/小さい, and he owner admits this is his own definition of 反対語 which is usable only on his site. He just could not find a better specific word, and ended up borrowing the word 反対語 for his own purpose.
Yoshinori Sakai, another amateur kanji researcher, published a book called 可逆語を探す in 2004, where 可逆語（かぎゃくご, literally "reversible word"） appears to be defined as a kanji compound that still makes sense when written in reverse order (again, not necessarily the same or similar meaning). But apparently almost no one have accepted this term after this book.