This is the 13098th most frequent German word.
allerletzten
"Allerletzten" means "very last" in English.
The word 'allerletzte' is used here as a superlative adjective to emphasize that this is the very last chance, with no possibility of another one.
Das ist meine allerletzte Chance, den Fehler zu korrigieren.
This is my very last opportunity to correct the mistake.
In this sentence, 'allerletzten' functions as an adjective modifying the noun 'Tag', to imply that it was the absolutely final day of the vacation.
Am allerletzten Tag des Urlaubs besuchte ich den Strand.
On the very last day of the vacation, I visited the beach.
Here, 'allerletzten' is used to stress that the cookies taken were the very last ones remaining.