Stoic “indifferent” by Zeno (founder of the school)
“Indifferent” has two meanings. In one sense [used by the Stoics] it signifies the things that contribute neither to happiness [eudaimonia] nor unhappiness, like wealth, fame, health, strength, and the like; for it is possible to be happy even without these things, though depending on how they are used they contribute to happiness or unhappiness. But in another [non-Stoic] sense “indifferent” signifies things that excite neither attraction nor aversion, as is the case with having an odd or even number of hairs on one’s head, or with extending or bending one’s finger. But it was not in this sense that the things mentioned above [such as health] are called “indifferent” [by the Stoics], since they are able to excite attraction and aversion. This is why some of the indifferent things are selected and others rejected, whereas indifference in the other sense provides no grounds for choosing or avoiding.
Diogenes Laertius, Life of Zeno