Immigrant visas are numerically limited by category and by country of chargeability (which is, in most cases one’s country of birth). What follows is the visa bulletin showing backlogs in each immigrant visa category.
The word “Current” indicates that no backlog presently exists in a particular category.
The dates in the Visa Bulletin can be misleading. Some dates, particularly in the Employment Based Categories, are “current” now, but may backlog before you can say “I-485”. Others, particularly in the Family Based Categories, look closer on the Bulletin than they are in reality. To see the rate of advance in a particular category, check the State Department’s Visa Bulletin.