Tether (often called by its symbol USDT) is a stablecoin cryptocurrency that is hosted on the Ethereum and Bitcoin blockchains, among others.
Its tokens are issued by the Hong Kong company Tether Limited,
which in turn is controlled by the owners of Bitfinex.
Tether is called a stablecoin because it was originally designed to always be worth US$1.00,
maintaining $1.00 in reserves for each tether issued.

Cloud mining is the process of cryptocurrency mining utilizing a remote datacenter with shared processing power.
This type of cloud mining enables users to mine bitcoins or alternative cryptocurrencies without managing the hardware.

The mining rigs are housed and maintained in a facility owned by mining company and the customer simply needs to register and purchase mining contracts or shares.

Since cloud mining is provided as a service, there is generally some cost and this can result in lower returns for the miner.