What does 3 pcs of contact lenses mean?

3 pcs/box = 1 pair + 1 piece of contact lenses

Contact lenses are usually sold in pieces and not in pairs, so 30 or 90 pcs for dailies, and 2, 3, 4, 6,10 or 12 pcs depending on the brand and because most users eye often differs from each other thereby requiring different dioptres for each eye.

Monthly lenses usually come in 2, 3, 4 or 6 pcs.

For example: In the case of a monthly lens, 2 boxes of 3pcs equals 3 pairs of lenses which last 3 months.