I'm not sure what it really means but i'll do a quick google.
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your baby might ‘drop’ (shift into your pelvis) before labor begins, but not all babies drop prior to the onset of labor. If your baby drops (this is also called ‘lightening’ or ‘settling’), you will begin to notice a decrease in lap space when seated, a sudden ease of breathing and more stomach capacity (since the load has shifted down), more pelvic pressure, and more frequent urination- maybe even slight incontinence. At each prenatal visit, your doctor will check to see if your baby has dropped into your pelvis.
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hope that helps.