Record Sets are a way in which to define in detail what, how, and when data should be synced to the Axsy Mobile App for offline use. Each Record Set defines the sync conditions of an Object (SObject) and optionally other Objects related to it. Record Sets can be defined for both Standard and Custom Objects in your Salesforce Org. 

You can create a Record Set for the Account Object (Account) to expand on what Accounts are synced to the app by default.