In typography, a paragraph is a block of text. Paragraphs are put on a new line and are usually indented, although not on many web sites, including Wikipedia. The paragraph symbol, the pilcrow, is ¶. In HTML, a new paragraph is created with the '<p>' tag, and the pilcrow symbol is ¶.
In literature, a detail is a small piece of information within a paragraph. A detail usually exists to support or explain a main idea.
For example, the following paragraph is an excerpt from Dr. Samuel Johnson's Lives of the English Poets. The first sentence represents the main idea, that Joseph Addison is a skilled "describer of life and manners". Further, each succeeding sentence is a detail that supports and explains the main idea.
As a describer of life and manners, he must be allowed to stand perhaps the first of the first rank. His humour, which, as Steele observes, is peculiar to himself, is so happily diffused as to give the grace of novelty to domestic scenes and daily occurrences. He never "o'ersteps the modesty of nature," nor raises merriment or wonder by the violation of truth. His figures neither divert by distortion nor amaze by aggravation. He copies life with so much fidelity that he can be hardly said to invent; yet his exhibitions have an air so much original, that it is difficult to suppose them not merely the product of imagination.
Notice that the main idea is a generalization, while each detail is a specific example of the generalization.
