What is "topness"

n. (context physics English) A quantum number of quark & hadron, determined by the number(s) of top quark present. Symbol ''T''.

Topness (also called truth), a flavour quantum number, represents the difference between the number of top quarks (t) and number of top antiquarks that are present in a particle:

$$T = n_\text{t} - n_\bar{\text{t}}$$

By convention, top quarks have a topness of +1 and top antiquarks have a topness of −1.The term "topness" is rarely used; most physicists simply refer to "the number of top quarks" and "the number of top antiquarks".