Tiddlers are the smallest unit of information in TiddlyWiki. Other systems have analogous concepts with more prosaic names: like "items", "entries", "entities" or "records". Even though "tiddler" is a bit of a preposterous name it has the virtue of being confusingly distinctive rather than confusingly generic.
Internally, tiddlers are an immutable dictionary of name:value pairs called fields. The only field that is required is the `title` field, but useful tiddlers also have a `text` field, and some or all of the standard fields listed in TiddlerFields.