The HTML <p> element (or HTML Paragraph Element) represents a paragraph of text. Paragraphs are usually represented in visual media as blocks of text that are separated from adjacent blocks by vertical blank space and/or first-line indentation. The paragraph must be closed at end of the text "<p> text </p>" are requried to put the text between the paragraph. Paragraphs are block-level elements.
The HTML <param> Element (or HTML Parameter Element) defines parameters for <object>.
The HTML <picture> element is a container used to specify multiple <source> elements for a specific <img> contained in it. The browser will choose the most suitable source according to the current layout of the page (the constraints of the box the image will appear in) and the device it will be displayed on (e.g. a normal or hiDPI device.)
The HTML <progress> Element is used to view the completion progress of a task. While the specifics of how it's displayed is left up to the browser developer, it's typically displayed as a progress bar. Javascript can be used to manipulate the value of progress bar.
The HTML Script Element (<script>) is used to embed or reference an executable script within an HTML or XHTML document.
The HTML <section> element represents a generic section of a document, i.e., a thematic grouping of content, typically with a heading. Each <section> should be identified, typically by including a heading (<h1>-<h6> element) as a child of the <section> element.
The HTML select (<select>) element represents a control that presents a menu of options. The options within the menu are represented by <option> elements, which can be grouped by <optgroup> elements. Options can be pre-selected for the user.
<spacer> is an HTML element which is used for inserting white spaces to web pages. It was created by NetScape for achieving same effect as a single-pixel layout GIF image, which was something web designers used to use to add white spaces to web pages, without actually using a GIF. However <spacer> is not supported by any major browser and same effects can be created with various CSS rules. In Mozilla applications, support for this element was removed in Gecko 2.0. Therefore usage of <spacer> is unnecessary.
The HTML Strikethrough Element (<strike>) renders text with a strikethrough, or a line through it. This element is obselete in HTML5. Use the <del> instead if the element is marking an edit (deleted text), otherwise use an <s> element.
The HTML <style> element contains style information for a document, or part of a document. By default, the style instructions written inside that element are expected to be CSS.
The HTML summary element (<summary>) is used as a summary, caption, or legend for the content of a <details> element.
The HTML template element <template> is a mechanism for holding client-side content that is not to be rendered when a page is loaded but may subsequently be instantiated during runtime using JavaScript. 
The HTML <textarea> element represents a multi-line plain-text editing control.
The HTML <title> element defines the title of the document, shown in a browser's title bar or on the page's tab. It can only contain text, and any contained tags are ignored.
The HTML Teletype Text Element (<tt>) produces an inline element displayed in the browser's default monotype font. This element was intended to style text as it would display on a fixed width display, such as a teletype. It probably is more common to display fixed width type using the <code> element.
The HTML <ul> element (or HTML Unordered List Element) represents an unordered list of items, namely a collection of items that do not have a numerical ordering, and their order in the list is meaningless. Typically, unordered-list items are displayed with a bullet, which can be of several forms, like a dot, a circle or a squared. The bullet style is not defined in the HTML description of the page, but in its associated CSS, using the list-style-type property.
The HTML Example Element (<xmp>) renders text between the start and end tags without interpreting the HTML in between and using a monospaced font. The HTML2 specification recommended that it should be rendered wide enough to allow 80 characters per line.
Each element in the top layer's stack has a ::backdrop pseudo-element. This pseudo-element is a box rendered immediately below the element (and above the element below the element in the stack, if any), within the same top layer.
The ::grammar-error CSS pseudo-element represents a text segment which the browser has flagged as having grammatical error(s).
The ::-ms-fill-lower CSS pseudo-element represents the portion of the "track" (the groove in which the indicator aka thumb slides) of an <input> of type="range", which corresponds to values lower than the value currently selected by the thumb.