Indentation in Python refers to the spaces or tabs used at the beginning of a line to define the structure and hierarchy of the code. Unlike many other programming languages, Python relies on indentation to indicate blocks of code, such as those within loops, conditional statements, functions, and classes.
Proper indentation is mandatory in Python, as it determines the grouping of statements and ensures the code is syntactically correct. Without proper indentation, Python will raise an Indentation Error. This makes the code more readable and structured.