Dart is a programming language developed by Google. It's used for building web, mobile, and desktop applications. Dart can be used to create both front-end and back-end code, and it's particularly known for being the language behind the Flutter framework.

In Dart, 'var' is used to declare a variable whose type is inferred from the value assigned to it. On the other hand, 'dynamic' is a type that represents a value whose type is not known until runtime. 'var' provides compile-time checks, while 'dynamic' skips compile-time type checks.

'async' and 'await' are used for asynchronous programming in Dart. 'async' is used to mark a function as asynchronous, allowing it to use the 'await' keyword. 'await' is used to pause the execution of the code until the awaited Future is completed, without blocking the whole program.

Mixins are a way to reuse code in multiple class hierarchies. A mixin is a class that provides methods to other classes but doesn't intend to be instantiated itself. To use a mixin, you use the 'with' keyword followed by the mixin's name when declaring a class.

In Dart, the 'main()' function serves as the entry point of the program. It's where the execution of the program starts. When you run a Dart program, the code inside the 'main()' function is executed first.