Question: What does the staggered line between metals and nonmetals on the periodic table represent?
About the article "Periodic table", section "Metallic character".

Candidate passages:
A dividing line between metals and nonmetals is sometimes replaced by two dividing lines.
One line separates metals and metalloids; the other metalloids and nonmetals. 
References to a dividing line between metals and nonmetals appear in the literature as far back as at least 1869.
In 1891, Walker published a periodic 'tabulation' with a diagonal straight line drawn between the metals and the nonmetals.
In 1906, Alexander Smith published a periodic table with a zigzag line separating the nonmetals from the rest of elements, in his highly influential textbook "Introduction to General Inorganic Chemistry."
In 1923, Deming, an American chemist, published short ([http://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=456 Mendeleev style) and medium (18-column) form periodic tables.
Each one had a regular stepped line separating metals from nonmetals.
Merck and Company prepared a handout form of Deming's 18-column table, in 1928, which was widely circulated in American schools.
By the 1930s Deming's table was appearing in handbooks and encyclopaedias of chemistry.
It was also distributed for many years by the Sargent-Welch Scientific Company. 
The dividing line between metals and nonmetals can be found, in varying configurations, on some representations of the periodic table of the elements (see mini-example, right).
Elements to the lower left of the line generally display increasing metallic behaviour; elements to the upper right display increasing nonmetallic behaviour.
When presented as a regular stair-step, elements with the highest critical temperature for their groups (Li, Be, Al, Ge, Sb, Po) lie just below the line. 
Depictions of metalloids vary according to the author.
Some do not classify elements bordering the metal-nonmetal dividing line as metalloids, noting that a binary classification can facilitate the establishment of rules for determining bond types between metals and nonmetals.
Metalloids are grouped with metals, regarded as nonmetals or treated as a sub-category of nonmetals.
Other authors have suggested that classifying some elements as metalloids "emphasizes that properties change gradually rather than abruptly as one moves across or down the periodic table".
Some periodic tables distinguish elements that are metalloids in the absence of any formal dividing line between metals and nonmetals.
Metalloids are shown as occurring in a diagonal band or diffuse region. 
Several terms are commonly used to characterize the general physical and chemical properties of the chemical elements.
A first distinction is between metals, which readily conduct electricity, nonmetals, which do not, and a small group, (the "metalloids"), having intermediate properties and often behaving as semiconductors.
A more refined classification is often shown in colored presentations of the periodic table.
This system restricts the terms "metal" and "nonmetal" to only certain of the more broadly defined metals and nonmetals, adding additional terms for certain sets of the more broadly viewed metals and nonmetals.
The version of this classification used in the periodic tables presented here includes: actinides, alkali metals, alkaline earth metals, halogens, lanthanides, other metals; metalloids, noble gases, polyatomic nonmetals, diatomic nonmetals, and transition metals.
In this system, the alkali metals, alkaline earth metals, and transition metals, as well as the lanthanides and the actinides, are special groups of the metals viewed in a broader sense.
Similarly, the polyatomic nonmetals, diatomic nonmetals and the noble gases are nonmetals viewed in the broader sense.
In some presentations, the halogens are not distinguished, with astatine identified as a metalloid and the others identified as nonmetals.