allerletzt
very last
Emphasizes that something or someone is definitively and without exception the last in a series or sequence.
Das war unsere allerletzte Chance, das Spiel noch zu gewinnen.
That was our very last chance to still win the game.

very last
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very last
Emphasizes that something or someone is definitively and without exception the last in a series or sequence.
Das war unsere allerletzte Chance, das Spiel noch zu gewinnen.
That was our very last chance to still win the game.

The prefix 'aller-' is used before superlatives to intensify them. It means something like 'of all'. It can also be formed with other adjectives, e.g. 'der Allerbeste' (the very best) or 'die Allerschönste' (the most beautiful of all).
Das war der allerbeste Kuchen, den ich je gegessen habe.
That was the very best cake I have ever eaten.
'Allerletzt' (very last) is a very strong form of 'letzt' (last). It emphasizes that there is absolutely no further possibility, person, or thing in a series. It expresses finality.
Ich gebe dir eine allerletzte Warnung.
I'm giving you one very last warning.
The adjective is often used in emotional or dramatic situations. Typical combinations are 'die allerletzte Chance' (the very last chance), 'der allerletzte Versuch' (the very last attempt), or 'im allerletzten Moment' (at the very last moment).
Er erwischte den Zug im allerletzten Moment.
He caught the train at the very last moment.
last
'letzt' and 'allerletzt' both refer to the end of a sequence. 'letzt' is the normal form: something comes at the end. 'allerletzt' gives stronger emphasis that nothing really comes after it, or that someone is at the very back of the line. Learners may confuse the words because they mean almost the same thing. If you only want to name the position at the end, 'letzt' is enough. If you want to emphasize the end especially strongly, 'allerletzt' fits better.

Paul kam als Allerletzter ins Ziel.
Paul crossed the finish line very last.
Am Montag besprechen wir den letzten Punkt auf der Liste.
On Monday, we will discuss the last item on the list.