Kefir and efir are nothing other than slang names for the Ethereum cryptocurrency.

A soft fork is a soft update of a cryptocurrency protocol that is compatible with older versions of the software, in which the network continues to operate as a single whole and is not split into separate chains.

Cloud mining is the renting of computing power from a third-party service to mine cryptocurrency without buying and maintaining your own equipment, which lowers the barrier to entry but increases dependence on the provider.

A node is a computer connected to a cryptocurrency network that stores blockchain data and verifies transactions according to the protocol rules, sustaining the operation of a decentralized system without a single center.

Mining is the process of confirming transactions and creating new blocks in the blockchain, for which network participants receive a reward in cryptocurrency in exchange for the computational work of their equipment.