The p tag is the paragraph tag. Every description text should be enclosed in a p tag. Only when there is only one paragraph (and no lists or tables or remarks) in a description node, then the p tag may be skipped.
Note that if a description node contains a table, pre, code or any list tag, then the text surrounding these tags must be put inside a p paragraph tag. This is different from the behaviour in HTML.
The paragraph tag must always have an opening tag and a closing tag, unlike html where only the opening tag may be present.
See also: table (180), dl (141), remark (174),code (135), ol (163),ul (192),ol (163)