help to explain

[chimcoin]

What’s the difference between Bitcoin-Qt and Bitcoin Core?

[mocacinno]

What’s the difference between Bitcoin-Qt and Bitcoin Core?

bitcoin core = the reference client, bitcoin-qt is a graphical "shell" of the reference client.
There are many wallets, many of them are good wallets with a nice feature set. Some are more user friendly, others have other pro's and con's... Core is the successor of the first client, initially written by satoshi. Since bitcoin is open source, p2p, core is not the "default" nor the "best" client out there (by defenition... in reality imho it's one of the best ones out there tough), it was however, the first one.

https://en.wikipedia.org/wiki/Bitcoin_Core
https://en.wikipedia.org/wiki/Qt_(software)

[Emoclaw]

Bitcoin QT was the previous name of the current Bitcoin Core client.
It was rebranded to Bitcoin Core in version 0.9.0 which was released in 19 March 2014.
At that version's release notes: https://bitcoin.org/en/release/v0.9.0#rebranding-to-bitcoin-core

[ZenFr]

What’s the difference between Bitcoin-Qt and Bitcoin Core?

There is no difference.
Only historic "rebranding".
Now "Bitcoin-Qt" is not used, only "Bitcoin core".
Qt is the name of a computer language/environment.

[100bitcoin]

What’s the difference between Bitcoin-Qt and Bitcoin Core?

Same. Mike Hearn named it Core.