### Translation:
1. **Naming**
` />`
2. **Usage**
When the selection is intended to be part of an SQL command: If the fields involved in the operation are numeric, then:
```php
if (!empty($_POST['checkbox'])) {
$expr = join(",", $_POST['checkbox']);
$sql = "SELECT * FROM tbl_name WHERE field IN ($expr)";
}
```
### Explanation:
- The first part shows how to create a checkbox input field in HTML, with its `name` attribute set as an array (`checkbox[]`) and its `value` dynamically assigned from PHP.
- The second part demonstrates how to handle the submitted checkbox values in PHP when constructing an SQL query, ensuring that the selected values are properly concatenated into a comma-separated string for use in an `IN` clause.