Google says:
If 5 finger widths of your baby's head is felt, it is written as 5/5 palpable or 'unengaged'.
If 4 finger widths of your baby's head is felt, it is written as '4/5' palpable or 1/5 engaged.
If 3 finger widths of your baby's head is felt, it is written as '3/5' palpable or 2/5 engaged.
If 2 finger widths of your baby's head is felt, it is written as '2/5' palpable or 3/5 engaged.
If 1 finger width of your baby's head is felt, it is written as '1/5' palpable or 4/5 engaged.
If your baby's head cannot be felt it is written as 'fully engaged' or 'not palpable'.
Most babies become 2 to 3 fifths engaged (or 2 to 3 fifths palpable) before labour commences, only becoming fully engaged during labour. If your baby is very active they may move 'in and out' of different levels of engagement during the last few weeks of the pregnancy, especially if this is not your first baby.
How long have you got to go?