A form of identification for when a certain transaction occurred.
Satoshi Nakamoto, the founder of Bitcoin, wrote in his whitepaper that timestamps aim to eradicate the threat of double counting.
Timestamps are an integral process in miners receiving compensation for mining each block.
This is because without the timestamp it would be difficult for new nodes to prove the difficulty, or lack of difficulty, or how long it took to mine a block.
To ensure difficulty is calculated accurately, blockchain stamps are used as opposed to real time.
When a BTC block is generated, two timestamps are usually involved.
One is the block header which is imputed by the miner.
The second is the actual at which the block was created.
While theoretically both should yield the same timestamp, there is always the slight risk of miners inputting incorrect times or lying about times.
Bitcoin has two ways of preventing this risk from happening.
The first is called the Median Time Stamp. The MPT rule stipulates the time stamp must be higher than the median value of the past 11 blocks.
The maximum allowable time difference between the time given by the node and local time system cannot exceed 90 minutes.
The purpose of the first rule is to ensure the blockchain moves forward in time while the second rule is aimed at preventing blockchain forward too much.
Both rules are aimed at protecting the integrity of cryptocurrency timestamps.