Open wifi (more correctl,y Wi-Fi) is any Wi-Fi connection that has not been configured with a password. Anyone with a Wi-Fi-capable device can connect to an open Wi-Fi hotspot.
If a password is used on a Wi-Fi connection, then the data being transmitted over the air is encrypted. Open Wi-Fi uses no password, and as a result, the data in transit is not encrypted. It can be easily viewed by anyone in range with an appropriate Wi-Fi capable device, such as a laptop, and packe- sniffing software.
Ask Leo! – How do I use an open WiFi hotspot safely?