This is the 9918th most frequent Russian word.
активностей
"Активностей" translates to "activities" in English.
In this sentence, 'активностей' is in the genitive plural form, describing the types of activities being offered.
Наш клуб предлагает множество активностей на выходных.
Our club offers a variety of activities on the weekends.
Here, 'активностях' stands in the prepositional plural form, specifying the context in which participation is required.
Для успешного завершения курса требуется участие во всех активностях.
To successfully complete the course, participation in all activities is required.
In this example, 'активностей' is in the genitive plural form, used to express the additional items being included.