blueline

[ bloo-lahyn ]
/ ˈbluˌlaɪn /

noun Printing.

a print made on light-sensitive paper and used as a proof for checking the position of stripped-up negatives or positives and copy prior to platemaking.
Also blue.

Origin of blueline

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019