In a law firm corporate and commercial are titles given to two related but usually separate groups. The distinction between the groups can differ across firms. The practice areas within corporate are closely linked and their work relates to the lifecycle of companies as well as mergers & acquisitions.
Commercial includes a broader range of practice areas such as franchising, intellectual property and sometimes litigation.
The common theme between these practice areas relates to issues arising from contract law. However, there are many similarities between commercial and corporate, especially in the type of work a trainee might do. Frequently practice areas from both groups work together on large transactions.