A "transfer" is commonly called a connection. Specific fares have limitations (restrictions) on how many transfers are pemited, where those transfers may take place, and what airlines may be utilized. Without such restrictions, an airline may un-wantingly sell a traveler a ticket from New York to Bogota with a transfer occurring in Paris. Or they might sell a ticket from Los Angeles to Bogota with transfers in Phoenix, Salt Lake City, St. Louis, Minneapolis, Chicago, Detroit, Atlanta, Washington, and New York. It is easy to understand why transfers are restricted.