ABAP Objects are the object-oriented extension introduced in 1999 to the original ABAP (Advanced Business Application programming) language and ABAP Workbench from R/3 release 4.6 and on.
This fully integrated extension endows ABAP with object-oriented features for the design and implementation of object-oriented programs. Programs in ABAP may or may not contain ABAP Objects, at the programmer’s discretion.
Techopedia explains ABAP Objects
With the introduction of ABAP Objects, SAP significantly enhanced the ability to design and develop large-scale applications using the objected-oriented methodology. ABAP Objects was not designed as an add-on, but rather as a fully integrated addition to the ABAP language. Accordingly, SAP introduced a new, enhanced virtual machine, capable of running both new applications implementing ABAP Objects and older ABAP/4 applications. Like other object-oriented programming languages, ABAP Objects provides full support for object features, including encapsulation, polymorphism and interfaces in a single inheritance model.