When sending a Z2Z (shielded-to-shielded) transaction, you're able to include a memo (message) in the transaction. This memo can be used for a number of different things.
Memos are primarily used for signing payments. Since shielded transactions encrypt your data, you're not able to see who sent you ZEC, and what the ZEC might've been for.
Users can use the memo field to sign their name or pseudonym to let their counterpart know who the transaction was from. They can also describe what the transaction was for.
Another use case for the encrypted memo is to send a message to someone with a z-addr. These messages can be about anything, whether it be a reminder to a friend, or a sensitive message that needs to remain as private as possible.
There was a person who sent their partner a love note in one of the first blocks in the Zcash blockchain. Someone found that their partner had sent them a file via a Zcash memo. This file was a ticket to a special event, overseas, that she and her distant lover had been talking about attending together.
<aside> 💡 The memo was a love note.
</aside>
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