Simply put ETF is an index fund that you can trade like stocks. Because it is a passive strategy (indexing), it has a very low management expense ratio (usually between 0.5% to 1%), there is no “load” and no early redemption charge.
hilo(still mellow)
There is tons of information you can find online, or books you can get from libraries. For starters, you can visit yahoo finance ETF center, and ishares.com