car park vs parking lot

car park and parking lot both are nouns.

Word	Noun	Adjective	Verb	Adverb
car park	Yes	No	No	No
parking lot	Yes	No	No	No

As nouns, car park and parking lot are synonyms defined as:

Other synonyms of car park include park, parking area.

car park (noun)	parking lot (noun)
a lot where cars are parked	a lot where cars are parked