The balance shown is your available balance against each account, including your arranged overdraft limit (if you have one) minus your pending card transactions.
This is different to some banking apps who don't include the arranged overdraft however you'll be able to see how much of your arranged overdraft you've used and how much you have left.
Pending transactions are debit card transactions that have been authorised but haven't yet been debited from your account e.g. pay at pump, hotel deposits. We include them in your balance but don't currently list them in the Business banking app. We're working on that.