An AST is usually the result of the syntax analysis phase of a compiler.
True, AST is drawn at the end of syntax analysis phase to find any syntax error in program.
AST has no impact on the final output of the compiler.
Wrong, It does have. Assume you missed semicolon in program, this is the phase where compiler gets warning to show you about error.
AST is a tree representation of the abstract syntactic structure of source code written in a programming language.
True, It's a code represented as tree.
AST is also used in program analysis and program transformation systems.
True, As explained above it is the one who helps analyses the program and gives syntax error according to programming language definitions.