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1.
A pun based on the word, Lumberjack, this phrase describes the act of masturbating and ejaculating onto the lower back (or lumbar region) of a woman.

Commonly performed by chiropractors while performing spinal adjustments.
This hot patient of mine wanted her spine adjusted so I took the opportunity for a quick lumbar jack. Ya, she sued, but I kept my license to practice.
by Reddition May 16, 2011