encapsulation
Wrapping data in one header after another as it goes down the layers, like envelopes inside envelopes.
Encapsulation is each layer treating the data from the layer above as its payload and adding its own header, so an MQTT message travels inside TCP inside IP inside a Wi-Fi frame.
Examples
Going down, the sensor's reading gets a TCP header, then an IP header, then a Wi-Fi frame header, like envelopes inside envelopes.
On arrival the laptop unwraps in reverse: frame header, then IP, then TCP, until only the JSON payload is left.