Single Level of Abstraction

Single Level of Abstraction (SLA): Each method should be written in terms of a single level of abstraction.

All statements of a method should belong to the same level of abstraction. If there is a statement which belongs to a lower level of abstraction, it should go to a private method which comprises statements on this level. Doing so will result in smaller methods.

Copied from here, can also read One Level of Abstraction per Function in book Clean Code: A Handbook of Agile Software Craftsmanship page 36