A set of characters enclosed within angular braces (<> or ) that develop a formatted command for a web page is called an HTML tag.

Yes, to both. In fact, both the header and footer tags are designed to serve their respective purposes in relation to whatever their parent “section” may be. So not only can the page body contain a header and a footer, but so can every article and section element. In fact, a header should be present for all of these, although a footer is not always necessary.