The Parallelization vertical tab allows you to configure parameters for partitioning a data flow into multiple threads, so as to handle those threads in parallel for better performance. The options that appear in this tab vary depending on the sequence of the row connection in the flow. In addition, different icons will appear in the row connection according to the options you selected.
Note that the Parallelization tab is available only on the condition that you have subscribed to one of the Platform solutions or Big Data solutions.
For further information about how to partition a data flow for parallelized executions, see Enabling parallelization of data flows.