I've received payment by echeque, what is it?
Paypal echeques are the bane of many sellers. They are usually generated when a buyer's payment card has expired, meaning that the payment is taken from their bank account instead. It then gets treated as a direct debit, and can take 10 days or more to clear. Don't send the item until you got an email from Paypal informing you that the echeque has cleared, as sometimes the payment will fail and you won't get the money.
It's also good to inform your buyer that they have paid by echeque as Paypal notoriously don't usually inform them, so they often become impatient wondering why you've not sent their item yet. Good communication will often keep your buyer happy. If they're in a hurry, you can cancel the payment from your Paypal account, and ask them to pay again once they've updated their payment details.