Commerce that takes place within a country, as opposed to between countries, which would be foreign or international commerce. For example a manufacturer of generic spare car parts in the UK that sells to factories based in the UK would be an example of domestic commerce.

noun. an interchange of goods or commodities, especially on a large scale between different countries (foreign commerce) or between different parts of the same country (domestic commerce) ; trade; business. Source: https://www.dictionary.com/browse/domestic-commerce