Transaction identifier (TX ID) also referred as Transaction hash is unique identifier of a particular transaction. TX ID is unique to the one given transaction in question.
You can find transaction ID in the transaction history of your Trezor Wallet/Suite or in transaction/withdrawal history of any wallet or service in general.
TX ID is used for identifying the transaction, by using this hash you can check the TX’s status and other transaction details (such as receiving address, fee height, transacted amount etc.) on the blockchain.
Revealing TX ID is no security issue but can be privacy sensitive (transacted amount, addresses)