Meaning
A small triangle pointing down, usually inside a square button, the same shape used for dropdown menus. It means down: lower, scroll down or look below.
It is the classic pointer to a link, comment or detail further down a post: “Full recipe in the comments 🔽” It also marks a small decrease or a section you can expand. For a dramatic plunge or “scroll to the very bottom”, ⏬ is stronger.