Generally this is in reference to the puckline, which is another name for the moneyline in other sports, or "spread betting". An team that finds themselves as an underdog to win outright might be seen as capable of holding their opponent within a certain amount goals, so the puckline is available for those who aren't sure of victory, but are sure of a solid effort. +1.5 in this context would mean that you expect the underdog to keep the score within two goals. The odds will be shorter than if you pick them for victory, but it's an avenue you can take with your NHL odds today if you aren't certain of victory (or, if you take the team at -1.5 - if you expect a big win)!