It's called compressed reserve. All your days off (typically 12) compressed into a single block. During your reserve days, they will call you every week or so & release you into 30 hours of rest to maintain legality for future flying assignments. You can bid in such a way that if you are awarded reserve and you bid compressed, you are guaranteed a compressed reserve line, even if it doesn't fall on the off days you requested. Stacking your days off so that one month's end rolls into the other's beginning is not guaranteed- and harder to accomplish- especially for the bottom guys.

The catch: you are NOT guaranteed a reserve line. At times on Guam, the bottom few pilots end up with forced lines made up of the least liked night trips. Reserve is usually junior, but not always "down to the bottom" junior. In June, the bottom 2 guys got lines- I have no idea if that was intentional. In May, RSV went all the way to the bottom. Compressing is an awesome option for traveling on your days off if you live in base, but I'd be pretty cautious about bidding Guam as a commuter- especially if you're junior.

There is also a way to waive some legality limits and compress a flying line. 10-12 consecutive days off used to be pretty easy to hit, but just from sheer lack of trips under COVID I'd imagine that's harder to do now, especially if you're junior.