(This post will be updated continuously based on everyone's contributions.) Note: This is the unofficial definition. People learn more about the material to understand more)
Blockchain
Chain-of-block technology, transactions are grouped into 1 block, blocks are joined to the chain following the block mechanism after saving the key hash of the previous block.
Consensus
Consensus algorithm, which is an algorithm that validates a block.
On-chain
Used to refer to tasks performed on Blockchain
Off-chain
Used to indicate tasks not performed on Blockchain
Cross-chain
Techniques for transferring tokens through different blockchain
Mainchain
Used to refer to the main blockchain, in a multiple blockchain group connected to each other.
Sidechain
Used to refer to the blockchain with a smaller ecosystem connected to the mainchain
Proof Of Work (PoW)
The consensus algorithm among the nodes in Blockchain, the consensus based on the effort (hash, hashing power) of the nodes.
Proof of Stake (PoS)
Synchronization algorithms between nodes in Blockchain, stencil-based relational representations of nodes.
Miner
Excavators, used to refer to computers participating in Blockchain, pack and confirm (Block).
Validator
Often, only the nodes involved create, confirm Block in Blockchain. Quite like Miner. This concept is used in Blockchain using the Proof Of Stake consensus algorithm.
Fork
Only splitting a blockchain into two or more branches, when two or more blocks are in the same block. Fork can be created accidentally, occurring when more than one miner digs a new block at the same time (will only exist temporarily), or deliberately, when the community breaks into two or more groups running the version Software incompatible.
Hard fork
It occurs when the consensus rule is loosened (if the old rule is a subset of the new rule), if all the updates update to the new software, then there will be no split, if there is one. The miner still running the old software will split.
Soft fork
Occurs when the consensus rule is tightened (the new rule is the subset of the old rule), if most of the miner update the new software, there will be no split, if only minor update will split.
Nothing at stake
Only happens when there is hard-fork. Because in PoS you do not have much energy to create a block, so you can create blocks at two chains at the same time.
Long range attack
This is because it does not take much effort to create a block so you can create your own chain, and your chain is longer than the main chain.
Thanks for the post, will probably be helpful for the newbies.
It's always frustrating to see threads like "what is a hard fork?" People can't seem to google nowadays.