The definition of bayān uses the terms dalālah (indication) and wuḍūḥ al-dalālah (clarity of indication). Without explaining indication, we cannot determine whether a meaning is communicated by a word's full established sense or by reference to a component or necessary concomitant of that sense.
The next foundational topic is therefore al-dalālah. Some signs connect to their meanings through linguistic convention; other signs work by observed or intelligible relationships.
This distinction prepares the learner for later discussions of literal expression, figurative usage, and allusion, where the link between an uttered word and the intended meaning requires careful analysis.