Definition 1

When the same information is presented in a different form that is easier to process, our ability to receive and remember it is greater. People often reorganize, regroup or compress information to aid in its understanding or recall. The resulting subgroups are ‘chunks’, which can be defined as a set of information or items that are treated collectively as a single unit (Mathy & Feldman, 2012).
In behavioral science, chunking has also been used to refer to breaking up processes or tasks into more manageable pieces (see for example Eşanu, 2019, on chunking in UX design or Wijland & Hansen, 2016, on mobile nudging in the banking sector).

Source: Behavioral Economics

Definition 2