"Rolling attacks" are a series of sequential attacks on the peloton by typically a team or a group of riders acting as a team. R. Chung covered this nicely in the comment section, but I will expand a bit here.
Typically you get two or three groups of riders together to orchestrate this (where a group may consist of one or more riders). The first group launches an attack (preferably when there is a lull in the peloton after a recent hard effort - gotta make it hurt to respond). They will either escape or the peloton hunts them down. The exact moment the first group is caught, the second group launches another attack. The moment they are caught the third or first group (depending on how many groups of riders you have) launches an attack. You then keep repeating as necessary or logical.
The idea behind doing this is that typically only a few riders (often tasked with this job) hunt down the breaks. If you have the manpower, by doing this you are working to wear out the other teams by brute force. Eventually, if you are lucky, the peloton may decide not to respond and you have yourself a break or you have tired out key players on the other teams. Again this only really works if you have a manpower advantage, leaving a few riders who are never involved with the attacks to conserve for the sprint or some other similar strategy.
As a caveat, I will add that I am not certain how much this strategy shows up in big shows (such as the Tour de France or Tour de Giro) as they know so much about the capabilities of the various riders, but I saw this was fair bit in our local racing scene.