Meaning of evolution in LTE (long-term evolution)
The only thing I can offer is that LTE's channel allocation scheme allows new modulation technologies to be used inside existing networks, so it is significantly more futureproof than GSM and UMTS.

In GSM, the frame format is rather fixed, so all that was possible for EDGE was to change the modulation for the data parts of the frame, leaving the control parts unchanged. Any valid EDGE frame is a valid GSM frame, except a listener that does not understand EDGE would get nonsensical data.

In UMTS, the code domain multiplexing significantly limits modulation choice, as symbols need to be stable for an entire period of the spreading pattern.

In LTE, subchannels and time slots are allocated and assigned to transmissions by the base station. Multiple adjacent subchannels can be combined, and there is no need to respect channel boundaries between combined channels or clear the channel at any point during a transmission or for anyone but the recipient to be able to decode the signal.

So in LTE, as long as the base and the mobile station agree on a transmission standard, they can use it without affecting any other station on the same network. New standards can be rolled out without interrupting service to older clients.

The 5G technologies we've seen so far don't really aim at replacing LTE, but at extending it to allow redirecting clients to other networks, e.g. a 5G base station could offer 802.11ad in the 58–60 GHz band as well, and announce this to stations.