Pending transactions are those transactions which were signed but are waiting to be executed and confirmed. You can see your pending transactions by going to the Transactions tab in the left side menu of your Ambire Wallet and view them under Pending transaction bundle. From there, you can either Cancel or Speed up the transaction by selecting a higher fee amount.
If you have transactions which were created but were not signed for any reason, you will be able to see those in the Transactions tab, under Waiting to be signed. Keep in mind that those transactions are not confirmed and are not referred to as Pending. Usually, transactions in this field are those who are part of a batch, created with the main aim of lowering transaction fees. More on transaction batching can be found in this article.