Invoices in Accounts Payable have status options of Approved, Pending and a checkbox indicating "Hold Payment".
If an invoice has a Pending status (regardless of being on hold) there is no ability to post or pay IF the business rule configuration is set to require approval to post or pay. A Pending status without the Business Rule marked will allow queries to pull for all pending invoices that they need to review or post.
If the Business Rule in Configuration is marked to "Require invoice approval before payment or posting" the Pending status will keep an invoice from appearing to post or pay. Only an invoice marked as Approved will appear for posting or payment with this rule in place.
If an invoice is marked "on hold" this will disable any payment to the invoice regardless of if it is approved or pending.