This is the 193rd most frequent Latvian word.
pirmajā
"In the first" (locative form of "pirmais").
Here, 'pirmajā' functions as a locative case of 'pirmais', indicating the temporal context of 'the first weekend'.
Grāmata tika izlasīta pirmajā nedēļas nogalē.
The book was read during the first weekend.
In this sentence, 'pirmajā' is used to describe the locative case referring to 'the first page'.
Pirmajā lapaspusē ir autogrāfs no autora.
On the first page, there is an autograph from the author.
This usage of 'pirmajā' represents the occurrence in the locative case of 'the first time'.