(rhetoric) an allegory, a fable (fictitious narration to enforce some useful truth or precept)

concept, general idea

(chiefly in mathematics, physics) for simplicity; for the sake of simplicity

ease / simplicity / lightness, brevity

easy / simple, uncomplicated / brief, light, short

complex (not simple or straightforward)

to use / to employ / to make use of, to apply / to spend

explanation

to explain

he / distal demonstrative, something far off removed from both speaker and listener: that / boyfriend