The first big Suzuki V-twin in this lineage was the TL1000S back in 1997. The TL stood for Totally Lunatic as the bike quickly gained a reputation for being a bit of a handful and was much loved by those of doubtful sanity. The DL still retains some of the character of the TL I.e. a sensible adventure bike that is a comfortable tourer but can also be ridden like a sports bike as well and has been known to upset plastic rockets on occasions. So perhaps it stands for Dual Lunatic, potentially schizophrenic?