Stablecoins are cryptocurrencies whose value is stable because they are backed by a real asset such as: USD (the US dollar), e.g., USDT (Tether), USDC (USD Coin), BUSD
A memecoin is a cryptocurrency created around a meme, a joke, or a viral trend on the Internet. They often have no real utility or solid technological project behind them. Their value depends heavily on public interest, trends on social media, and speculation.