Batch sparging drains the mash tun completely, adds all the calculated sparge water in one addition, stirs thoroughly to re-mix the grain bed, and drains again — a fundamentally simpler process than fly sparging's continuous, carefully-matched drain-and-add technique.
The efficiency trade most homebrewers accept happily
Batch sparging typically extracts a few percentage points less sugar for the same total water volume than a carefully executed fly sparge does, because it doesn't rinse the grain as thoroughly or as gradually. Most homebrewers find that gap easy to accept in exchange for a faster, simpler, far more forgiving process — a batch sparge is much harder to get wrong on brew day than a fly sparge, which needs continuous attention to keep the add-rate and drain-rate matched.
Two batches, or one — a real recipe decision
Some batch-sparge recipes call for a single sparge addition; others split the sparge water into two smaller batches (a "double batch sparge"), draining and re-adding twice, which recovers a bit more sugar than a single large addition would. Either approach is a legitimate batch-sparge variant, and the choice mostly comes down to how much extra time a brewer wants to spend chasing marginal efficiency gains on a given brew day.