sellotape

Sellotape is the UK brand name for transparent adhesive tape, now used generically (like Scotch tape in the US). Not concerning, just stationery vocabulary. If your kid uses it constantly, ask them where they first heard it, not to police their speech but to understand which online community they are in. Most slang of this kind moves through TikTok and group chats, so seeing it in your child's vocabulary just means they are plugged into normal teen internet culture.

Sellotape is the UK brand name for cellulose adhesive tape, used generically (like American "Scotch tape"). Use in British English contexts. Formal equivalent: "adhesive tape," "clear tape." Common non-native mistake: capitalisation. Even though it is a brand name, in current British usage it is often lowercased ("sellotape") as a generic noun and verb. Capitalisation depends on context. Read or listen to the word in context several times before trying it yourself; the right register is harder to learn than the dictionary meaning.