This is the 2nd most frequent Malay word.
di
"Di" is a preposition in Malay meaning "at," "on," or "in," used to indicate location or position.
In this sentence, 'di' is a locative preposition indicating place or location, specifying where the book is placed.
Buku itu diletakkan di rak.
The book is placed on the shelf.
Here, 'di' again serves as a locative preposition to denote the location where the child is playing.
Anak itu sedang bermain dan berseronok di taman.
The child is playing and enjoying in the park.
In this context, 'di' is used as a locative preposition indicating the country where the speaker has resided.