ETF stands for Exchange Traded Fund. It's just a fund listed on stock exchanges that have the blessing of the SEC. Basically it lets an organization buy shares of something like gold, oil, corn, foreign currency, etc. You can have a futures ETF which trades on speculative prices not tied to the real asset, like oil futures (essentially state-sanctioned gambling). However, this Blackrock ETF is interesting because it is a spot ETF, meaning in order to sell "shares" of bitcoin on stock exchanges, they need to have that amount of bitcoin as collateral. They will need to buy actual bitcoin to sell their ETF "paper" bitcoin to investors.