AB

"AB" means a blood type of the abo system that has both blood antigens and may receive all blood types, and donate to ab. 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.

"AB" is informal English meaning a blood type of the abo system that has both blood antigens and may receive all blood types, and donate to ab. It is used widely across English varieties. A more formal or neutral equivalent would be something like "a blood type of the abo system that has both blood antigens and may receive all blood types" expressed in standard vocabulary. A common mistake is to assume "AB" can replace its standard equivalent in every register; keep it for spoken or casual situations and use the formal form in writing.