Transaction

j"1NF7i6ZoMDXaJ2Q5M9QFriH74ya6r6vP8u Block HashMWhile the previous answer is very detailed, I would like to add that double hash is a reference to the block hashing algorithm. Simplified, you can say that the block header is hashed (which also contains the hash tree reference to all the TXes in the block). This has is then taken and hashed again. This block hash is acceptable as long as it meets the criteria. One of them is difficulty. If the hash is a too large number, it is rejected, so miners also don't broadcast it. Transactions are not double hashed according to my knowledge.