Exchange Traded funds (ETFs) have become an increasingly popular investment option over the last couple of decades. There is now over $4 trillion worth of assets that are invested in ETFs worldwide. The largest and oldest ETF, the SPDR S&P 500 (SPY) has nearly $237 billion in assets and is consistently one of the most highly traded securities in U.S. exchanges. In spite of this, I’ve found that many investors are still kind of confused on what exactly an ETF is. Many times, they’ve heard about them, but are still kind of fuzzy on the details of how they work…