Yapper means: Someone who talks too much, especially online. From 'yap' . 2024-25 vintage. Affectionate when said about yourself; cutting when said about someone else.. It is internet-era slang, commonly seen on TikTok, Discord, Reddit or X. There is no real cause for parental concern; it is descriptive vocabulary rather than risky behaviour. If your teen uses it, context will usually make the intent clear. A short, curious question about where they heard it is usually all that is needed to know whether to follow up.