If a buyer pays you through paypal, they can choose to pay you by an eCheque. An eCheque is where the money is taken from the buyers bank account, then put into their paypal account which is then paid to you for the item that they bought. This whole process usually takes around 10 to 14 working days.
Do not send out any items until the payment is showing as 'Cleared' and you can see that the funds are in your paypal account as sometimes eCheques do fail!
You can choose not to accept eCheques in your paypal account, but so far I haven't had any problems with them and I do get a lot of customers who pay with them.
Hope this helps you !!