th elements are very commonly used to indicate headings for table rows and columns, like so:

<table>
    <thead>
        <tr>
            <td></td>
            <th>Column Heading 1</th>
            <th>Column Heading 2</th>
        </tr>
    </thead>
    <tbody>
        <tr>
            <th>Row Heading 1</th>
            <td></td>
            <td></td>
        </tr>
        <tr>
            <th>Row Heading 2</th>
            <td></td>
            <td></td>
        </tr>
    </tbody>
</table>

This can be improved for accessibility by the use of the scope attribute. The above example would be amended as follows:

<table>
    <thead>
        <tr>
            <td></td>
            <th scope="col">Column Heading 1</th>
            <th scope="col">Column Heading 2</th>
        </tr>
    </thead>
    <tbody>
        <tr>
            <th scope="row">Row Heading 1</th>
            <td></td>
            <td></td>
        </tr>
        <tr>
            <th scope="row">Row Heading 1</th>
            <td></td>
            <td></td>
        </tr>
    </tbody>
</table>

scope is known as an enumerated attribute, meaning that it can have a value from a specific set of possible values. This set includes:

References: