I assume you're referring to Breaking Dawn? In that case, EJ stands for Edward Jacob, what Bella would have named her baby had it been a boy.
"ej" doesn't have a universal or commonly known meaning or abbreviation. It could potentially stand for specific things in certain contexts, but without more information, it's difficult to provide a definitive answer.
E is Edward and J is Jacob.
Edward Jacob or Edward Junior it is not confirmed in the book
EJ Caillouet goes by Ej, and Eeej.
Ej Sepp's birth name is EJ Sepp.
The "EJ" in Captain E. J. Smith stands for "Edward John".
It's not "WW". It is "EJ" and represents the designer of the coin, Elizabeth Jones.
Kanam EJ died in 1982.
Ej Linehan is 5' 8".
Ej Sepp is 6' 3".
Holden EJ was created in 1962.
EJ Assi is 5' 10".
EJ Caillouet is 5' 11".