Well, they are supposedly rankings, with BR essentially being the top. They added a new TR class this year, which is supposed to be the team category. Originally they had a bunch of rules regarding the TR category, like each team had to field a min. (6) number or riders etc. However, quite a few teams cant field 6 men in the TR category, so the JBCF relaxed the rules.
For example, at the east Japan race at Gunma CSC a couple months ago ALL of the pro teams except Blitzen could not meet the min. entry requirements for TR so the JBCF changed that rule. On the other hand, Ravanello came with 15 riders of various levels and pretty much all but 2-3 of them were pack fodder or spit out the back.
It seems that the Japanese federations are into making pointless rules that only make entering the races more difficult or pointlessly splits up races in the name of "safety". Basically they seem to go as far as they can to ignore what racers want: appropriate length (most are WAY too short) and a decent number or competitors in each category.
In the US its a simple 5,4,3,2,1, Pro with most races combining races to increase field size such as (5,4) (3) (Pro,1,2) with 3`s usually having the biggest fields.
I would love to see Japanese federations lower the barriers to racing (same day entry etc.), but so far they seem intent on making things complicated.
TR= Tour Racer
BR1= Businessman racer 1
BR2= Businessman racer 2 (level 2, slower than BR1)
BR3= Businessman racer 3 (like a cat. 4 in the states)
ER= Entry Racer
FR= Feminine racer
There is a lot of crossover though. For example, if you look at the last results from the Fuji HC, you see that almost half of the BR1 racers placed better than TR racers (with exception of top 8 or so). BR2 guys also would have placed higher than a majority of TR.