The act of manually rummaging through archived forums, BBSs, news groups, etc., in search of useful information.
The term is frequently used figuratively in an effort not to reveal the specifics of one's resources (ie: what site you got the information from. See second example).
NOT to be confused with Dumpster Diving (Dumpster Diving was recently incorrectly defined on Al Franken's nationally syndicated radio show.)
'You'll never guess what I found Board Walking yesterday!'; 'So I found a list of credit card numbers on the Board Walk this morning...'