Keywords are reserved words with special meaning: if, else, for, while, def, class, import, etc.

Identifiers are names for variables, functions, classes, etc. Rules:

• Start with letter or underscore
• Contain letters, digits, underscores
• Case-sensitive
• Cannot be keywords

# Valid identifiers
variable_name = 10
_private_var = 20
ClassName = "example"

# Invalid identifiers
# 123variable = 10  # Cannot start with digit
# class = "test"    # Cannot use keyword