Hotspot
Your mobile phone has an internet connection via your mobile provider network. With the hotspot feature you can share this internet connection with other nearby devices. Your mobile phone can become a personal wireless router and allow multiple devices to simultaneously use its cellular data network. Again, your wireless carrier may require additional service fees and configurations in order to enable the hot spot capability on your mobile phone.
Tethering
Tethering is the process of connecting a secondary device to your mobile device in order to use your mobile device’s Internet/data connection on the secondary device. For example, you can connect your computer to your mobile phone via a USB cable and your computer can now have access to the Internet via your mobile phone. Tethering can also be configured via a wireless Bluetooth link.
Additional service fees or configuration may need to be done by your wireless carrier in order to enable tethering.
Whereas a hotspot allows multiple devices to use your mobile phone’s cellular data network simulaneously, tethering just provides a single connection to a single external device at a time.
Airplane mode
Your mobile device may have a variety of wireless connectivity options (Cellular, WiFi, Bluetooth, NFC, GPS, etc.) Airplane mode allows you to enable or disable all of these features simultaneously. Your mobile device’s wireless signals may cause audible interference with an aircraft’s radios, and therefore it is required that you turn on your mobile device’s Airplane mode during take off and landing in an airplane. Turning on Airplane mode will disable all wireless connectivity, but you do have the option to re-enable individual features. For example, if your airplane features Wi-Fi, you can leave Airplane Mode on, but re-enable just your Wi-Fi connection.
On iOS devices, the Airplane Mode can be enabled/disabled via the Settings or the Control Center.
On Android devices, the Airplane Mode is accessible via the Settings and then Wireless & Network Settings.