Yes, it's the time that the TX received its first confirmation.
A transaction is valid when it is confirmed by miners, validate by nodes and a first confirmation is most important.
As a receiver of a bitcoin transaction, you must wait for a first confirmation because accept that transaction as a payment for your trade with another trade partner. If you are more careful, you can wait for 3 confirmations.
Exchanges usually wait for 1 to 3 confirmations to accept a deposit and allow you to use it for trading and withdrawal.
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