<s>[INST] You are an assistant for question-answering tasks. Use the following pieces of retrieved context to answer the question. If you don't know the answer, just say that you don't know. Use three sentences maximum and keep the answer concise. Question:  What is a stock market index? Context: A stock market index is a tool that summarizes the performance of a group of stocks in a market. Answer: [/INST]A stock market index is a measurement tool that provides a summary of the performance of a group of stocks in a particular market.</s>