What is Dynamic HTML?
Reviewing the W3C 'Document Object Model' section http://www.w3.org/DOM/, it's clear what the W3C sees as 'Dynamic HTML'. The current specification details an 'open' standard object model that allows total document and content manipulation, that all elements (even those not directly supported by the browser) within the document are programmable objects with support for mouse and keyboard events, that all the document content can be manipulated (content added, changed or removed 'on-the-fly', without a return trip to the server) and that the document style sheet settings are also exposed as programmable objects, allowing stylings to be changed on-the-fly. As such, it represents a significant enhancement to static HTML and also to currently available 'dynamic' methods (i.e. scripting, server-side scripting/CGI etc.) 'Dynamic HTML' is apparently supported by both Microsoft and Netscape in Internet Explorer 4.0 and Communicator 4.0. An 'open' standard supported by both browsers...surely this is too good to be true...

Implementation differences
Yes, it is!
Netscape's implementation of 'Dynamic HTML' revolves around a slightly enhanced scripting object model, dynamic style sheets (through proprietary Javascript style sheets), absolute positioning (primarily through the use of layers - see <LAYER> and <ILAYER> and the Layer Object for all style sheet positioned elements). Netscape does support full CSS positioning of elements, but their position can only be manipulated by working through the Layers collection - and dynamic fonts (allowing fonts to be embedded in pages and downloaded along with them). Microsoft's implementation revolves around a significantly enhanced object model, dynamic style sheets (through the W3C standard CSS object model), absolute positioning (for all elements) and also implements some of the finer points of what 'Dynamic HTML' should be by allowing direct document and content manipulation (the ability to add, remove, or change any element or content). Essentially, Microsoft have fully embraced the 'Document Object Model concept and HTML 4.0, previously known as Cougar, for support in Internet Explorer 4.0.
To see what the W3C envisage as 'Dynamic HTML', visit http://www.w3.org/TR/WD-DOM/requirements.html, as mentioned above, a document that details the requirements of the 'Document Object Model' - the name the W3C is using, where Microsoft and Netscape use 'Dynamic HTML'.

Dynamic HTML specifics
The following pages detail the various standard 'Dynamic HTML' properties, methods and events. Note that most of these are supported for almost every possible HTML element by Internet Explorer, with Communicator support being somewhat more limited. The details are basically an overview (with examples) of the properties, methods and events. For element/object specific properties, methods and events (and relevant browser support details), see the specific element/object topics.

Dynamic HTML Sub-Topics
Standard DHTML events
Standard DHTML methods
Standard DHTML properties
Dynamic data binding
Visual filters