The <b> tag is an HTML element used to apply bold formatting to text. When the <b> tag is used to enclose a section of text, that text will be displayed in a bold font weight in most web browsers.

The <i> tag is an HTML element used to apply italic formatting to text. When you wrap a section of text in <i> tags, that text will be displayed in an italicized font in most web browsers.

In HTML, the term "sub" refers to a markup tag used to represent subscript text. The "sub" tag is used to indicate that the text enclosed within the tag should be displayed at a lower position than the surrounding text, typically used to denote mathematical subscripts or chemical symbols.

In HTML, the "iframe" (short for "inline frame") element is used to embed another HTML document or web page within the current document. It allows you to display content from another source within your web page, while still retaining control over the styling and layout of that content.

In HTML, the "colspan" attribute is used to specify the number of columns that a table cell should span. This attribute is used in conjunction with the "td" or "th" elements to define the layout of tables.

In HTML, the "rowspan" attribute is used to specify the number of rows that a table cell should span. This attribute is used in conjunction with the "td" or "th" elements to define the layout of tables.