800 number

"800 number" means a toll-free telephone number. It is one of many casual words teens pick up from friends, social media, music or sport, and on its own it carries no particular warning. If you hear your teen use it, it is fair to ask what they mean by it in their friend group, since meanings drift quickly. Asking out of curiosity rather than alarm tends to keep the conversation open and useful.

"800 number" is informal English meaning a toll-free telephone number. It is used widely across English varieties. A more formal or neutral equivalent would be something like "a toll-free telephone number" expressed in standard vocabulary. A common mistake is to assume "800 number" can replace its standard equivalent in every register; keep it for spoken or casual situations and use the formal form in writing. If you are a B2 or C1 learner, it is useful to recognise this word when you hear or read it, but think carefully about whether the situation really calls for it before using it yourself.