This is the 1616th most frequent Russian word.
хорошего
"Хорошего" means "good" or "the good" as a form of the word "хороший," often used in the genitive case.
In this sentence, 'хорошего' is used in the genitive case as an adjective agreeing with the noun 'дня' (day). It means 'good' in the sense of pleasant or positive.
Желаю вам хорошего дня.
I wish you a good day.
Here, 'хорошего' is in the genitive case and qualifies the noun 'отдыха' (rest). It implies quality or enjoyment.
У нас есть всё для хорошего отдыха.
We have everything for a good rest.
In this instance, 'хорошего' modifies 'настроения' (mood) in the genitive case. It denotes a positive or uplifting quality of mood.