Definition of rundown
In French, one could translate rundown by montante. But let's say that the use of the word "rundown" is quite marginal. A rundown is, in Omaha, the succession of 4 cards in a row. If you receive 2-3-4-5 or 5-6-7-8 in your four card hand, you have a rundown. You can have rundown offsuit, single suited or double suited. For example, 2-3-4-5 with four different suits is a rundown offsuit. If you have, say, 2 spades among your 4 cards, you have a suited rundown and if you have 2 spades and 2 clubs, say, you have a double-suited (DS) rundown.
How strong is a rundown?
A rundown is a relatively strong hand. Obviously, the higher your rundown, the stronger it will be. And if you have a matching double rundown, it will be even stronger. The reason for the strength of these hands is that they connect very well with several boards. Let's imagine a rundown like 4-5-6-7 on a 6-7-2 flop. Not only do you have two pair, but you also have a straight draw. And if the board was more like A-K-J, these hands would be easy to play; you'd just fold of course.