I need to know if it is BACKBITING to say unwanted things in a WhatsApp group chat, where the person is not texting in the conversation/may not be present but is a member of the group chat.Please explicitly state wether it is halal or haram.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad, sallallaahu 'alayhi wa sallam, is His slave and Messenger.

Backbiting (Gheebah) is defined as speaking ill of someone in their absence, as clarified in the authentic Sunnah. This definition applies to the situation you described. The fact that the person discussed is a member of the (whatsApp) group does not exempt the situation from being considered backbiting, as the negative remarks were made in his absence. The possibility that he might later learn of this conversation does not change the nature of the act as backbiting.

Allah knows best.