A hardware wallet, also called a Cryptocurrency safe, is one of the safest storage results. A hardware wallet is a device that can be connected to the computer via the USB port or another connection and on which you can store your Bitcoins or Altcoins. You can also send or receive currencies via this wallet.
Storing coins on a hardware wallet is also called Cold storage. Cold storage means that you have access to your wallet (private key) stored offline and all online files deleted. There are various other forms of cold storage, such as a paper wallet, brain wallet or a wallet on an offline computer.
The currently available hardware wallets contain, besides the storage of the wallet, advanced security applications to protect your Bitcoins in an online environment. How extensive these applications are varies by brand and type. The safest types are also the highest priced.