Polysemy refers to the phenomenon where a single word has multiple related meanings. For example, the word "bank" can refer to a financial institution or the side of a river. Understanding polysemy is important for language learners to develop accurate comprehension and use of vocabulary. Teaching polysemy involves providing context, using visual aids, and practicing with sentences that illustrate different meanings. Activities might include matching exercises, context-based vocabulary practice, and exploring word origins to understand the connections between meanings.