This is the 7300th most frequent French word.
niçois
Relating to Nice or its inhabitants.
Here, 'niçois' is used as a noun, referring to the people who live in or originate from Nice.
Les niçois célèbrent le Carnaval chaque année.
The people of Nice celebrate the Carnival every year.
Here, 'niçoises' is an adjective derived from 'niçois' and agrees in gender and number with 'plages'. It describes the beaches as belonging to or characteristic of the city of Nice.
Les plages niçoises sont magnifiques.
The beaches in Nice are magnificent.
In this sentence, 'niçois' is used as an adjective to describe the man's origin, specifically that he's from Nice, a city in southern France.