A whitelist is a subjective measure that a blockchain node can put into effect to allow transactions to be put into a block only if they are listed on their author (account) or contract whitelist. Each node can specify their own whitelist, and these are not publicly viewable. Even if a node does not have the author/contract on their whitelist, it will still accept the transaction as valid if another Block Producer places the transaction into a block. To completely block transactions that are not on the whitelist from being added, all Block Producers will need to have the same whitelist settings at all times. Whitelist takes precedence over blacklist. Watch our video explanation.
Greylisting an account means that this account will only have access to the amount of resources for which it has delegated. When the blockchain is under-utilized, users and dapps may utilize a portion of the unused bandwidth of the chain. However, a greylisted account will always be limited to their objective limits.
A microfork occurs when a Block Producer begins to produce blocks with the same block height as a block that was recently produced. This is often the result of high latency between producing nodes, which may occur from time to time. Since this is a small divergence in the flow of blocks on the blockchain, this is known as a microfork. There is very little cause for concern, and microforks should be almost undetectable to the average user. Watch our video explanation.
When there are any changes made to the consensus mechanism on the blockchain, there needs to be a hard fork to demarcate this change in the software that is run by both validating and non-validating nodes. Any node that does not upgrade their software will no longer be able to accept blocks from the new part of the chain.
In blockchain, to burn a token is to make it unusable. This is typically done by sending the token to an account with a nulled key (cryptographically inaccessible). However, since EOSIO allows 15 of 21 Block Producers to access tokens on an account that has nulled keys, it is best to burn tokens by using the retire function to remove the tokens from circulation completely. Further, since inflation is based upon the total supply, tokens burned by sending to a nulled account, but not those burned with the retire action, will still be included in the circulating supply.