Frequency means remembering the kanji by writing them out numerous times or remembering them through frequent use.
1 I remember kanji by writing them out numerous times until I know them
2 I remember the kanji which I use often
e.g.1 名前 (なまえ name) “I often have to write this” (student).
e.g.2 車 （くるま car） “I remember that one because we use it quite often” (student).
e.g.3 家 （いえ house） It appears in a lot of things so I just remember it” (student).