In Flask Python, an identifier can be

In Flask, a Python web framework, an identifier can be a variable name used to identify a route, function, or a part of the application. It's a string of characters that is unique within the scope where it's used.

Here's a step-by-step explanation:

1. Flask uses routes to handle URLs. These routes can have variable parts, which are marked as <variable_name>. This variable_name is an identifier. For example, in @app.route('/user/<username>'), username is an identifier.

2. The function that's associated with a route (the one that's decorated by @app.route) can also have an identifier. This is its function name. For example, in the following code, show_user_profile is an identifier:

@app.route('/user/<username>')
def show_user_profile(username):
    # show the user profile for that user
    return 'User %s' % username

3. Inside this function, you can also have identifiers for variables. In the above example, username inside the function is an identifier.

4. Flask also uses identifiers for its different components, like app in app = Flask(__name__).

So, in Flask Python, an identifier can be a route variable, a function name, a variable inside a function, or a component of the application.