Logical flow of information
The logical order results from the logical document structure. It is the clear and linear order in which the information flows logically from one section to the next. It has nothing to do with the position of objects on a page.
Logical order = reading order
You can check the logical order by viewing the tag tree. The arrangement of the tags form the logical order. Roughly speaking the logical order is equivalent with the reading order (e.g. for assistive technologies).