The <th> tag is used to mark table header cells. By default, most browsers display the content of header cells in bold and centrally aligned, while regular font is used to display content in other data cells.^[1]

Another function of the table header markup is that it's crucial for accessibility. Screen readers announce headings as users move through the table, giving assistive technology users the context that is available to visual users at a glance. Failing to use the correct markup for table headers, you'll make the table navigation nearly impossible for assistive technology users.