Originally Posted by Paypal Transaction Page

The money from the payment you received is being held temporarily for up to 21 days. During this time the money will show as pending and you won't be able to access it.

Your funds will be released after 21 days, providing your buyer hasn't reported any problems. We may be able to release the money sooner if we can confirm that the item was delivered or, if this is an eBay item, your buyer leaves you positive feedback.
To help speed up the process, please take the following steps:

1. Check below to see if this transaction is eligible for seller protection. For more information, see our tips on how to sell securely
2. Ship to the buyer's address as stated on this page
3. If your item is over £150 please use a shipping service which offers signature confirmation
4. Save all proof of shipping, and email tracking information to your buyer