You may have heard about the #AppleEcosystem and wonder what it is. What I've personally have heard the most is it's iMessages, but there's a little more to it than that. iMessage and AirDrop are the two I can think of which is for more people; AirDrop is a way to share content easy and fast, much like Bluetooth back in the flip phone days. What makes AirDrop great is ease of use, you just press the recipient in a list, once they accept, the content is on the recipient device almost instantly. When AirDropping to a device which share Apple ID, there's no need to accept the content.
Some of the other easy to name parts of the ecosystem ties into AirDrop. My favourite being universal pasteboard, allowing me to copy something on any of my Apple devices and paste it on any other Apple device, I use this all the time for Two Factor Authentication. As with iMessage, I can also send old-school SMS from my Mac, this is done over the iPhone, likewise I can also take and initiate old-school phone calls from my Mac.
These are only the tip of the iceberg of what the ecosystem is, but this is what I use on the daily, and misses every time I'm not at my Mac!