The item you're asking about is a Philips Avent Natural Nipple designed for use with their Natural bottles.1Here's a breakdown of the information based on the code you provided:Avent Nipple Natural: This refers to the Philips Avent Natural bottle range, which features a wide, breast-shaped nipple to promote a natural latch, making it easier to combine with breastfeeding.21M+: This is the recommended age range for the nipple, meaning it is suitable for babies 1 month and older.31S: This likely refers to a Single Pack (1-piece) of the nipple, although most retailers primarily sell them in 2-packs.Flow Rate: For the newer Natural Response nipples, a flow for 4$1\text{m}+$ is often designated as a Flow 3 nipple.5 For the older free-flow Natural nipples, a 6$1\text{m}+$ nipple is typically a Slow Flow (often marked with "2" or "Slow").7Key Features of the Philips Avent Natural Nipple (either version):Shape: Wide, breast-shaped for a natural latch.8Material: Soft, durable silicone.9Anti-Colic: Integrated anti-colic valve designed to vent air away from the baby's tummy to reduce discomfort.10