ping pong vs Ping-Pong

ping pong and Ping-Pong both are nouns.

Word	Noun	Adjective	Verb	Adverb
ping pong	Yes	No	No	No
Ping-Pong	Yes	No	No	No

As nouns, ping pong and Ping-Pong are synonyms defined as:

ping pong and Ping-Pong: a game (trademark Ping-Pong) resembling tennis but played on a table with paddles and a light hollow ball

Other synonyms of ping pong include table tennis.

ping pong (noun)	Ping-Pong (noun)
a game (trademark Ping-Pong) resembling tennis but played on a table with paddles and a light hollow ball	a game (trademark Ping-Pong) resembling tennis but played on a table with paddles and a light hollow ball