What is a tab position?  This refers to the spot (position) that an individual tab falls in a bank of tabs.  For instance, the numeral 1 in a 1-25 bank set (collated) is in the top or 1st position, numeral 2 is in the 2nd position and so on to numeral 25 in the 25th position. 

Since numeral 26 starts back at the top again, it is considered to be in the 1st position.  The most commonly used tabs are available in sequential sets (collated) as well as by individual numbers in a single position.