Batch processing groups data from a period and processes it together on a schedule, with higher latency. Streaming processes each event (or small windows of events) as it arrives, with low latency.
In DP-900: the monthly accounting close is batch; detecting fraud as it happens or monitoring sensors is streaming. Streaming uses time window aggregations (tumbling, sliding, or session windows).
Batch vs. stream processing is a concept that can show up on the exam. Check the full guide to see it in context.