heraldry vs emblem

heraldry and emblem both are nouns.

Word	Noun	Adjective	Verb	Adverb
heraldry	Yes	No	No	No
emblem	Yes	No	No	No

As nouns, emblem is a hypernym of heraldry; that is, emblem is a word with a broader meaning than heraldry:

heraldry: emblem indicating the right of a person to bear arms
emblem: special design or visual object representing a quality, type, group, etc.

heraldry (noun)	emblem (noun)
emblem indicating the right of a person to bear arms	special design or visual object representing a quality, type, group, etc.
the study and classification of armorial bearings and the tracing of genealogies	a visible symbol representing an abstract idea