What does #1 mean?

According to ICV2 Pathfinder is the #1 selling RPG and it has been the #1 line for the last year.

Top 5 Roleplaying Games – Spring 2013
	Title	Publisher
1	Pathfinder	Paizo Publishing
2	Dungeons & Dragons	Wizards of the Coast
3	Star Wars	Fantasy Flight Games
4	Iron Kingdoms	Privateer Press
5	Dark Heresy/Rogue Trader/Deathwatch	Fantasy Flight Games

Top 5 Roleplaying Games – Fall 2012
	Title	Publisher
1	Pathfinder	Paizo Publishing
2	Star Wars	Fantasy Flight Games
3	Dungeons & Dragons	Wizards of the Coast
4	Dark Heresy/Rogue Trader/Deathwatch	Fantasy Flight Games
5	Iron Kingdoms	Privateer Press

Top 5 Roleplaying Games – Summer 2012
	Title	Publisher
1	Pathfinder	Paizo Publishing
2	Dungeons & Dragons	Wizards of the Coast
3	Dark Heresy/Rogue Trader/Deathwatch	Fantasy Flight Games
4	Dragon Age	Green Ronin Publishing
5	Dungeon Crawl Classics	Goodman Games

Top 5 Roleplaying Games – Spring 2012
	Title	Publisher
1	Pathfinder	Paizo Publishing
2	Dungeons & Dragons	Wizards of the Coast
3	Dark Heresy/Rogue Trader/Deathwatch	Fantasy Flight Games
4	Dragon Age	Green Ronin Publishing
5	Marvel Heroic Roleplaying	Margaret Weis Productions

According to Inc. Paizo Publishing is ranked #2370 of the top 5000 list.

2013 STATISTICS

Rank: 2370

3-year growth:152%

2012 Revenue:$11.2 million

2009 Revenue:$4.4 million

Web site:Paizo.com

Employees: 42

Jobs added, prev. 3 years:17

Founded: 2002

Location:Redmond, WA

Industry: Retail

There is quite a bit of information and speculation to be gleaned from these simple information bits. This kind of information should also help explain why Hasbro is expanding the license of D&D continually into boardgames, lego like toys, video games and other non-rpg fields.