Dictionary entry
perplexity
also PPL
Definition of perplexity
-
: a measure of how surprised a probabilistic language model is by a sequence of tokens, commonly calculated from its average negative log-likelihood; lower perplexity means the model assigned higher probability to the observed text
- The new checkpoint achieved lower perplexity on the held-out corpus.
- The teams did not compare the two perplexity scores directly because the models used different tokenizers.
Two meanings, one word
In everyday English
A state of being confused or puzzled.
In AI
A measure of how surprised a probabilistic language model is by a sequence of tokens, commonly calculated from its average negative log-likelihood; lower perplexity…
Origin & history
Perplexity predates modern large language models and has long been used to evaluate statistical language models. It can be understood as the model's effective uncertainty among possible next tokens on a particular dataset.
Test yourself
Which of these is the meaning of perplexity?
Cite this entry
"Perplexity." AI Dictionary, Dadgogo, https://dadgogo.com/dictionary/perplexity/. Accessed 7 Oct. 2026.