Difference between ABAP and HR-ABAP

In HR-ABAP, we make use of existing(Standard or custom) macros, selection screen, function modules..etc to retrieve data from DB, the same task can be even done by simple ABAP statements but we have some important reasons to go for existing programs.
To simply say HR-ABAP is also ABAP where existing FMs, macros,LDBs...etc are designed specially to retrieve HR-DATA.
Before getting into HR-ABAP technically, we have to know about some concepts which are specific to SAP-HR and some terms where we have not used much while working with ABAP.
concepts:Info-types,LDBs,macros, provide/endprovide statement and Authorisation checks.