If someone is shown to be On-line in WhatsApp inside the actual Chat we previously had, does that mean they've opened that particular chat OR that they're simply "Online"??
Online and last seen tell you if your contacts are online, or the last time they were using WhatsApp.
- Online means that the contact has WhatsApp open and is connected to the internet. However, it does not necessarily mean the contact has read your chat.
- Last seen refers to the last time the contact used WhatsApp.