BLEU score was published by Papineni et. al. 2002 in their research publication named BLEU: a Method for Automatic Evaluation of Machine Translation (https://www.aclweb.org/anthology/P02-1040.pdf). BLEU stands for Bi-Lingual Evaluation Understudy. For a given machine-generated output (say translation in the case of machine translation or summary in the case of text summarization), the score measures the goodness of the output, that is, how much close the machine-generated output is to any of the possible human-generated references (possible actual outputs). Thus, the closer the output text is to any human-generated reference, the higher will be the BLEU score.
The motivation behind BLEU score was to ...
