Unlike what many people think lel is not an acronym in the same fashion that LOL is (it does not mean laughing extremely loud, laughing extra loud or similar). Lel (and variations including lal) resulted from the use of random vowels substituted in place of the 'o' in LOL. These vowels were used in an attempt to be different from the millions of internet game fags. The word however, in essence, still means LOL.
guy1: generic xyz funny comment
guy2: lel wtf