Each year, teams have the option (and why they wouldn't use it boggles the mind) to roll over any unused salary cap space from the current season on to next year's cap. It is helpful, of course, buying a little more space with which to use the following season. The NFL Players Association released the list of each team's rollover money for 2017 Wednesday. The Cardinals have slightly more than $4.4 million they are carrying over for 2017, which just means they will tack on $4.4M to whatever the salary cap is this season.
That number has yet to be set (although reports have it going from $155M to between $166M and $170M). Until then, it's tough to know how much cap space the Cards will have going into the offseason. It's safe to say the Cardinals won't have a ton to spend, not with their own free agents they are trying to retain and the raises others are due this coming season.
The $4.4M rollover is the second-largest amount in the NFC West. The Rams have only $305,000 or so, and the Seahawks are at $2.07M. But the 49ers rolled over a massive amount -- $38.7M -- which will give them a ton of room to play with. (Amazingly, that's not the most rolled over in the NFL. The Jaguars are rolling over $39.3M, and the Browns are rolling over a whopping $50.1M. Of course, you have to have places to spend that cap space to make it mean anything.)
Figuring out exact cap space is always a tricky thing, although the NFLPA does attempt to release the information when the new league year (and free agency) starts. It's frequently a moving target, especially in the offseason with the top 51.