Testnet

How Do Testnets Work?
The term "testnet" refers to a separate blockchain where new features can be implemented without endangering the main network.
If new tools or products aren't rigorously tested under a variety of conditions before being added to a live blockchain, there could be serious implications. In the worst situation, flaws could appear that hackers could exploit, costing individuals money.

Developers continue to search for faults when a testnet is active. Additionally, they might ask a few people to test the blockchain in order to receive helpful input.

After been tested on a testnet, a feature may then be added to the mainnet. Decentralized networks, on the other hand, can require that ecosystem participants be given the chance to vote first.
Additionally, testnets can offer a useful simulation tool that enables users to experiment with cryptocurrencies and attempt new things risk-free.

Coin

Cryptocurrencies known as coins run on separate blockchains and are unrelated to other coins. Such a cryptocurrency's single unit is also known as a coin.

Pair

Exchange cryptocurrencies with each other, like the trading pair BTC/ETH.

Candidate Block

In a few words, a candidate block is a block that a mining node (miner) is trying to mine in order to receive the block reward. So a candidate block may be described as a temporary block that will be either validated or discarded by the network. Miners compete with each other to validate the next block and add it to the blockchain, but first, they have to create a candidate block to participate in the mining competition.