Syntax
The grammar rules for how Python code must be written.
Syntax is the set of grammar rules every Python program must follow: a colon after an if, for, or def line; consistent indentation for the block underneath; and matching quotes and brackets. Break a rule and Python reports a SyntaxError and refuses to run the file at all — nothing executes until it's fixed.
# Correct syntax: a colon, then an indented block
if 3 > 2:
print("valid Python")
# Missing the colon would raise, before anything runs:
# SyntaxError: expected ':'
Output
valid Python
Where this shows up in real Python
Syntax governs every line you write. A syntax error stops the program before it runs at all, unlike a runtime error that happens mid-execution.
Official documentation: Python Tutorial: Syntax Errors