Invalid syntax in Python refers to a situation where the code you have written does not conform to the language's syntax rules. In other words, the Python interpreter is unable to understand and execute the code because it does not follow the proper structure and rules of the Python language.

When you encounter invalid syntax in Python, it means that there is a mistake in the way you have written your code. This could be a missing parenthesis, a misplaced colon, an incorrect indentation, or any other violation of Python's syntax rules.

For example, if you write something like:

```python

print "Hello, world!"

```

You will encounter invalid syntax because in Python 3.x, the print statement requires parentheses:

```python

print("Hello, world!")

```

Common causes of invalid syntax errors in Python include:

1. Forgetting to close parentheses, brackets, or quotes.

2. Using incorrect indentation.

3. Misspelling keywords or functions.

4. Mixing tabs and spaces for indentation.

When you encounter invalid syntax errors, Python will typically provide a helpful error message that points to the specific line and character where the error occurred. This can be very useful for debugging and fixing the issue.

To resolve invalid syntax errors in Python, carefully review your code and look for any mistakes that violate the language's syntax rules. Pay close attention to indentation, punctuation, and the correct usage of language elements such as keywords and functions.

In summary, invalid syntax in Python simply means that your code contains errors that prevent it from being understood and executed by the Python interpreter. By understanding and following Python's syntax rules, you can avoid these errors and write clean, error-free code.