Definition of DS
Unlike Hold'em where it's good news to receive cards that are both the same suit, in Omaha it's bad news. If you receive four cards in spades or four cards in hearts in Omaha, it's bad news because you know you're less likely to hit your flush. However, if you have a double-suited hand, it's good news. The fact that your hand is double-suited will add equity. For example, if you have a hand like 5-6-7-8 unmatched, you will have 42% equity against a random hand. But if you have 5-6-7-8 double-suited, you will now have 49% equity against a random hand.