Gold or silver ETFs (Exchange-Traded Funds) are funds which hold physical gold or silver, and sell shares of the fund on the open market much like a stock. The share owner is paid in cash on redemption in most cases. Those ETFs that allow bullion redemption typically only do so in lots of 100,000 shares (over $15 million) typically, and only through a broker. Be aware that some ETFs hold futures contracts, not physical bars, as backing for their shares.
Doug Eberhardt's article "Turning Paper Into Gold" at Seeking Alpha explains the pros and cons of precious metals ETFs versus owning physical gold and silver, and things to be aware of. It's well worth a read!