This is the 2980th most frequent Russian word.
детства
"Детства" means "childhood" (genitive case of "детство").
The word 'детства' refers to the speaker's period of childhood in a genitive case, indicating origin or association.
У меня много воспоминаний из детства.
I have many memories from my childhood.
The word 'детстве' is in the prepositional case, indicating the time of the speaker's childhood during which the described action took place.
В детстве я любил читать книги.
In childhood, I loved reading books.
The word 'детства' once again is in the genitive case, showing possession or connection to the concept of childhood.