According to Douglas Hoffstader's book, Gödel, Escher, Bach: An Eternal Golden Braid, i-mode is one of the three modes of human action ( the other two being m-mode and u-mode ).

A person is working in "intelligent mode" when actions are based on observation, deduction, logic, and any other intellectual abstraction.

For example, that act of trying to determine someone's E2 password by looking at their homenode and attempting to guess what they might use is acting in intelligent mode.