what is topic modeling used for code example

Example: topic modeling in Machine learning

def lemmatize_stemming(text):    return stemmer.stem(WordNetLemmatizer().lemmatize(text, pos='v'))def preprocess(text):    result = []    for token in gensim.utils.simple_preprocess(text):        if token not in gensim.parsing.preprocessing.STOPWORDS and len(token) > 3:            result.append(lemmatize_stemming(token))    return result