A blockchain is a public distributed ledger that is used to make transactions and save the transaction data on the network by using cryptocurrency by a group of computers that participate in the network called nodes.
A block is a unit of data on the blockchain used to represent money and other kinds of data like certificates. Each block on the blockchain contains the hash value of its preceding block and this iterative process makes all blocks on the blockchain connected to each other. The hash value of each block is uniquely generated based on its contents and the hash value of a block changes if its contents are changed which will change the contents of its succeeding block making the whole chain invalid. This acts as a security feature against any attempt at manipulation of data on the blockchain network.
Proof of Work
Proof of work is a mechanism where miners on the blockchain network compete to solve a complex mathematical problem faster than the others in order to be able to successfully perform a transaction and to be able to add a new block to the blockchain.
The miner who solves the mathematical problem faster than others and successfully adds a new block to the blockchain receives a reward. Since the mathematical problems are usually hard to solve, hashing and proof of work mechanisms together provide security to the blockchain network.
Longest Chain is a long single chain of blocks which usually happens when several nodes manage to successfully complete the proof of work mechanism resulting in hard forks. When a new block is added to one of these forked chains, it becomes the longest chain and the other forked chains are considered invalid by the blockchain network and the data on those blocks in sent into the transaction pool to be added into another new block.
A wallet is a blockchain component used to store the transaction data and the private information of its owner securely by generating and using a pair of public and private keys.
A distributed network is a network formed by a group of computers or nodes interconnected on the network without any central authority. On blockchain networks, each participant on the network gets a full copy of the updated central ledger and any changes made to the data can be easily identified thereby providing security to the blockchain network.