It's the Hash (ie sha256^2) of the transaction in little-endian
For example, the Hash of
I imagine for this transaction hash for example is shortened to like 5bc9eb then hashed with the previous block, (read farther down on that wiki page, theres the merkle tree root information there, it takes the previous blocks Merkle and hashes it with the transaction. So say the merkle for this block was "hashMerkleRoot=e81287" (which is the hash of the previous blocks transactions, to provide a chain order?) and our transaction is "hash=5bc9eb", the hash of the two of those is the actual "hash=" that is stored in the block you see which could be "hash=2d7f4d"