This is the 6151st most frequent Russian word.
существования
The word "существования" in English means "existence."
The word 'существования' ('existence') is used here as a noun in the genitive case, denoting the concept being questioned.
Мир часто задаёт вопросы о смысле существования.
The world often questions the meaning of existence.
In this instance, 'существования' refers to the circumstances surrounding existence, again in the genitive case, showing possession or relation.
Условия существования на планете сильно изменились.
The conditions of existence on the planet have changed significantly.
'существования' is used to specify the subject being studied or discussed ('existence'), appropriate to its genitive case to match the preposition 'о'.