Can I cancel a bitcoin transaction if it has no confirmation?

If the transaction has no confirmations yet, there’s still a chance that you can cancel it. There are two primary strategies you can use to try to cancel your unconfirmed Bitcoin transaction: Some wallets support the RBF protocol allowing you to replace your original transaction with a new one that includes a higher transaction fee.

Can I cancel a bitcoin transaction if I'm unable to use RBF?

If you’re unable to use RBF, you still may be able to cancel the Bitcoin transaction by double spending with a higher fee. To do this, make a new transaction equal to the amount of the original one and send it to yourself. Make sure the transaction fee on this is significantly higher than the original one you paid.

What are bitcoin transactions?

Bitcoin transactions are messages, like email, which are digitally signed using cryptography and sent to the entire Bitcoin network for verification. Transaction information is public and can be found on the digital ledger known as the 'blockchain.'

Can I cancel a transaction sent from a web wallet?

You can't "cancel" a transaction sent from a web wallet, and RBF/double-spend is also not possible from web wallet. There is nothing you can do, your funds are lost. Actutally there is one thing you can try, there is a slim chance that this might work though.