This is the 5219th most frequent Polish word.
ras
The Polish word "ras" means "race" (as in a biological or social group).
In this sentence, 'raz' is used to refer to a single occurrence or a moment in time that happened once.
To był raz, kiedy byłem na plaży podczas deszczu.
That was once I was at the beach during rain.
Here, 'ras' is the plural form of 'race', referring to different ethnic groups or categories of people.
Ludzie różnych ras mieszkają w tym mieście.
People of different races live in this city.
In this instance, 'raz' is used as part of a frequency expression ('raz na tydzień'), meaning 'once per week'.