Towards the end of your pregnancy, your midwife will feel how far your baby's head has moved down into your pelvis. She'll then describe in fifths how much of your baby's head can be felt above the brim of the pelvis. If all of the head can be felt, it's described as 5/5 palpable. If it's engaged, it would be 2/5.
With a first baby, the head often engages before labour, but this isn't usually the case with subsequent pregnancies. Some women say they can feel when the head has engaged, or 'dropped', as their bump feels lower and they've less pressure under their ribs.
Anne Richley, midwife.