XHTML Terminology

  elements
  tags
  open tag
  close tag
  self-closing tag
  attributes

  types of elements 
  [Source: Cascading Style Sheets: The Definitive Guide, 2nd Edition, sect 1.3]
       replaced (e.g. img) vs. non-replaced (almost everything else)
       block-level (e.g. p, div) vs. inline-level (e.g. em, span)

       CSS can define block vs. inline level for XML elements
  
  proper nesting
  parent and child