What is the accuracy majority class classifier? I have an SFrame and a model:

train_data,test_data = products.random_split(.8, seed=0)
selected_words_model = graphlab.logistic_classifier.create(train_data,
                                                     target='sentiment',
                                                     features=selected_words,
                                                     validation_set=test_data)


After computing the accuracy of the model with `selected_words_model.evaluate(test_data) I'm asked "What is the accuracy majority class classifier on this task?" Yet I don't even know what this "means accuracy majority class classifier", shouldn't it be "accuracy of the majority class classifier" ?

Here is my attempt.

All these materials come from this coursera ML fundations course exercise.
I suspect you are right that there is a missing "of the," and that the "majority class classifier" is the classifier that predicts the majority class for every input. Such a classifier is useful as a baseline model, and is particularly important when using accuracy as your metric. This matches what your notebook comments in the next bullet, so that's likely what was intended.