A web site is a set of web pages and hypertexts links. The contribution of this paper is a description of web sites also called web documents as a structured object with a logical and a physical structure. Indeed, it will show that the web document can be divided into geometrical blocks (physical structure) and furthermore each page of a site has an individual function, each can be classified within a meaning (logical function). An application of this object is also described using an eye-tracking experiment. For this experiment, some web documents was studied with the same methodology than that used for paper documents. Two eye-tracking results are developed and for each the usual meaning for document and the signification in the context of web documents will be described. The results show the strong relationship between the structure and the user perception of web document. Two eye-tracking data were derived from the results: the number of fixation per web document and the number of blocks (pages) seen are both correlated with structure descriptors.