AND-SPLIT and OR-SPLIT in AEM Workflow
AND Split allows execution of all the branches configured in parallel
The workflow will go to next step(in this case "Last Step") only if the execution of all the branches is completed.
For example, you can allow certain review steps to occur in parallel, so saving time.
The OR-Split allows you to introduce a conditional path processing in your workflow. The decision is based on the result of Routing expression. For whichever branch, expression returns true that particular branch of OR Split would be executed. The first script that evaluates to true is executed.