How do you access the query string in Flask routes?

How do you access query parameters or the query string in Flask routes? It's not obvious from the Flask documentation.

The example route /data below illustrates the context that I would like to access that data. If someone requests something like example.com/data?abc=123, I would like access to the string ?abc=123 or to be able to retrieve the value of parameters like abc.

@app.route("/data")
def data():
    # query_string = ???
    return render_template("data.html")