There are many ways of identifying the extent and progression of prostate cancer. Cancer in general is listed as stages 1-4, and this can also be applied to prostate cancer, but it is often not what people are referencing. Here is one link that provides some further information (and correlation) without getting too far into the details. https://www.cancer.org/cancer/types/prostate-cancer/detection-diagnosis-staging/staging.html
1. At that link you will find that "Grade group IIB" correlates with a "gleason score of 3+4."
2. Gleason scores refer to cell analysis under a microscope of removed samples, either biopsies or slices of a prostate. In general, they are talking about the most abnormal (cancerous) sample when only one is given. 1 and 2 are considered in the normal range, 3-5 indicate increasingly abnormal cells.
3. The first number is the most common in the sample, the second is the second most common. So 3+4 is better than 4+3, even though in a different scheme they might both be referred to as 7.
4. Since biopsies get graded as 3+3 up to 5+5, one scheme is to renumber these as 1 through 5, where 1 is 3+3...and 5 is 5+5. If this were the scheme, over 1 is beyond 3+3, and 3 is 4+4.

But wait, there's more! Another way of looking at prostate cancer (pc or sometimes in the literature PCa) is low risk, intermediate risk, and high risk based on the aggressiveness of the cancer. In the staging table above, intermediate are the II's (a, b, and c). However, there's a big difference among intermediate risk cancers, so they can be split into intermediate favorable (lower risk) and intermediate unfavorable (higher risk). While there are other criteria, initial diagnosis based on biopsy would split between intermediate favorable (3+4=7) and intermediate unfavorable (4+3=7). As you might guess, when more abnormal (cancerous) cells predominate in a sample, there is more likelihood of spread beyond the prostate.

Lastly, here is a link basically describing the 4 (5) stages of cancer. https://www.webmd.com/cancer/cancer-stages
There are five if you include the zero stage. Once it is detected, it is always at the stage detected. If you want to correlate, generally stage 2 is intermediate unfavorable, stage 3 is spread to nearby lymph nodes or other tissue at the margins of the prostate, and stage 4 is elsewhere, typically many other places in the body--prostate cancer eventually spreads to the bones. The label sticks with where the cancer cells initially came from, because it indicates the type of abnormal cells spreading, so cancer in the bones that started in the prostate is metastatic pc, which is another name for stage IV prostate cancer.