Definition of High-Low
If we take the case of Omaha High-Low, there is not always a Low, but there is always a High. For example, if the board is J-J-A-K-Q, we know that there will be no Low because we will need 5 cards smaller than an 8 including the hole cards. In this situation, the player with the High will win 100% of the prize pool. If at the showdown two players have the same Low and player number 1 also has the High, player number 1 will win 75% of the prize pool and player number 2 will win 25% of the prize pool.