Stopwords are common words in a language that do not carry much meaning, such as "the", "and", and "of". In natural language processing tasks, removing stopwords is a common preprocessing step. This is because eliminating these words can improve the accuracy and efficiency of various algorithms and techniques applied to text data.

NLTK provides a built-in set of stopwords for several languages, including English, French, German, and Spanish. These stopwords can be easily removed from text using NLTK's stopwords module. By doing this, the resulting text data is left with only the most meaningful words, which can significantly enhance the performance of algorithms used in tasks like sentiment analysis and topic modeling.