Can someone explain what is the meaning of Approved Change Requests?

From PMP point of view an Approved Change Request is a Change Request that has undergone Integrated Change Control Process.
This also means, the change has been analysed for it's impacts, Risks, Scope and the Change Board (including sponsor/customer) is happy to accept the changed scope/time/cost/Quality/HR/Customer Satisfaction implications.

This eventually means that the Project Manager now needs to update the performance Measurement Baselines (Cost/time/scope) to reflect the approved change.

This would mean the Project Manager would need to change every single Project Management document that is impacted by the approved change - HR Management Plan if resources are added/removed , Scope Management Plan and all relevant scope items - WBS, WBS-dictionary as scope is changed, Cost Management Plan , if Budget is changed, Schedule Management Plan and all relevant schedule documentation .

This will happen as outputs of DIRECT AND MANAGE Project work process, an execution process.

In organizations with well defined customer requirements, a Change Request is a formal request from the customer to change a deliverable or otherwise somehow change the scope of a set of requirements. Once submitted by the customer, it is reviewed by the project and the level of effort (and thus the cost difference if any) is determined and communicated back to the customer. Once the customer accepts to take on the financial repercussions and and delivery impact it may carry, it is an Approved Change Request and once codified properly within the SOW and the companies legal and contractual practices, can be scheduled for inclusion in the project.