Bullshit answer for something you don't want to explain, go into detail on, or if it's something you really have no idea as to the cause of.
"How'd you do that, Mark?"
"Look Mr. Frodo, real elf magic!"
"How'd you guess that? No one's ever guessed that before. How'd you know?"
Elf magic is a word that can be used to explain anything that you don't feel like going into detail on, or something that defies proper explanaition.
Basically a bullshit answer.
"ur xplanation is the xact answer...no1 has evr said that b4...howd u know that was the answer?"
"Why, the rope isn't broken, Sam!"
"Real elf magic, Mr. Frodo!"