形迹 has two main clusters of meaning: (1) a person's bearing, demeanor, or outward appearance — most often seen in the set phrase 形迹可疑 ('look suspicious'); (2) a trace, sign, or vestige left behind, either physically (脚印 is a literal footprint but 形迹 is more figurative, like 'signs that something happened'). A third, less common usage is 'formal courtesy' as in 不拘形迹 ('without formality'). The gloss 'formality' from the dictionary refers to polite social behavior, not to official procedures. Context tells you which sense is meant.