Blockchain - 51% Attack - Cryptocurrency

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We can break 51% Attack term in simply as 51% and Attack.

Now 51% illustrates the majority in a group of 100%.

For example, we have 100 people who are going for the voting where only two candidates are having for selection.

Now when the total number of votes is 100, so the winning number should be minimum is 51.

i.e. out of 100% at least 51% of people should be in favour of the winning case.
If it is 50-50 then it's a tie which has no results and for less than 50% or 49% or below leads to denial for the acceptance.

An attack is defined as by techopedia.com :

An attack is an information security threat that involves an attempt to obtain, alter, destroy, remove, implant or reveal information without authorized access or permission.

Attack 51%

Now, let's discuss how this impacts the user/network transactions in the blockchain.
Blockchain works in a form of the distributed ledger where every transaction is available on the network for all users for review and approves or deny.

It is a chain block for the execution for every transaction which includes various blocks to perform.
Once a block has finalised either approve or deny it cant be altered.

Now for the same to obtain 51% approval or denial for any transaction whoever tries to attack 51% needs to have the impact on the 51% of the blocks to have an impact on the transaction.

It is usually said that if 51% network is also accessed to alter the transaction its low in probability for the success.