phase line

noun

: a line (as a terrain feature extending across the zone of action) used to control and coordinate a military advance or withdrawal

the regimental commander may prescribe any phase lines

—Infantry Journal

reach a phase line one mile inland by 1600 hours

—Irwin Shaw

—abbreviation PL

Love words?

You must — there are over 200,000 words in our free online dictionary, but you are looking for one that’s only in the Merriam-Webster Unabridged Dictionary.

Start your free trial today and get unlimited access to America's largest dictionary, with:

• More than 250,000 words that aren't in our free dictionary
• Expanded definitions, etymologies, and usage notes
• Advanced search features
• Ad free!