What is classed as 'Foreign income' for the purposes of tax

We are UK based and offer items for sale within the UK, however we have had a handful of customers from abroad contact us and have subsequently sold to them. The transactions are through PayPal and are invoiced in Stirling, received in Stirling with not VAT charged (we aren’t VAT registered). Are these classed as Foreign income for the purposes of tax or is Foreign income only income earned as a result of work, etc carried out in a foreign country…?