The WhatsApp broadcast is a one-to-many messaging feature on WhatsApp. With one single message, you can therefore reach many users at once.
Unlike WhatsApp groups, where all members see all the messages and responses, messages that you send through a broadcast list, end up in the recipients' private chats.
And if they answer you, the conversation stays between the two of you, and isn't public, like in the group.
In order to send out a WhatsApp broadcast, you need to set up a broadcast list.
This can be done on the WhatsApp Business App and the WhatsApp Business API, as the private WhatsApp is off limits for business use!
However, the Business App has very limited functionalities, which is why the API is the better option for most businesses.