QT

Qt (Cute) is a cross-platform application framework that is widely used for developing application software.


Qt Creator provides a cross-platform, complete integrated development environment (IDE) for application developer.


idgets are the basic building blocks for graphical user interface (GUI) applications built with Qt. Each GUI component (e.g. buttons, labels, text editor) is a widget that is placed somewhere within a user interface window.


MOC(meta object compiler)

The Meta-Object Compiler, moc, is the program that handles Qt's C++ extensions.
The moc tool reads a C++ header file. If it finds one or more class declarations that contain the  Q_OBJECT macro, it produces a C++ source file containing the meta-object code for those classes. Among other things, meta-object code is required for the signals and slots mechanism, the run-time type information, and the dynamic property system.


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QML stands for Qt Meta Language or Qt Modelling Language is a user interface markup language.

What is a slot? And how it differs with callback Method?

Slots are normal C++ member functions and can be called normally; their only special feature is that signals can be connected to them. A slot is called when a signal connected to it is emitted. We can also define slots to be virtual.

Surely more than on slot can be connected to a single signal. Then Slots are called in the order they are connected when the signal is emitted.