Stars and Stripes vs American flag

Stars and Stripes and American flag both are nouns.

Word	Noun	Adjective	Verb	Adverb
Stars and Stripes	Yes	No	No	No
American flag	Yes	No	No	No

As nouns, Stars and Stripes and American flag are synonyms defined as:

Stars and Stripes and American flag: the national flag of the United States of America

Other synonyms of Stars and Stripes include Old Glory, Star-Spangled Banner.

Stars and Stripes (noun)	American flag (noun)
the national flag of the United States of America	the national flag of the United States of America