The algorithm described in this paper is designed to detect potential table regions in the document, to decide whether a potential table region is, in fact, a table, and, when it is, to analyze the table structure. The decision and analysis phases of the algorithm and the resulting system are based primarily on a precise definition of table, and it is such a definition that is discussed in this paper. An adequate definition need not be complete in the sense of encompassing all possible structures that might be deemed to be tables, but it should encompass most such structures, it should include essential features of tables, and it should exclude features never or very rarely possessed by tables.