IJLA is shorthand for "I Just Laughed Audibly". IJLA can act as an alternative to, or qualifyer for LOL.
Often one will write LOL in a text message, but because of the ubiquity of the term, it can be helpful to follow it up with IJLA if you actually made a sound, rather than simply typing LOL, which can appear simply as an appreciation of your own or another's wit.
IJLA let's people know that you just laughed audibly.
Friend: *something funny*
You: LOL!!!!
You: IJLA hahahaha
Or
Friend: *something funny"
You: IJLA