Definition of Nepotism: "Favoritism granted to relatives or friends regardless of merit".
Someone, whose father is a captain and has taken him/her to flights on Cessna since kid and told stories in dinner table from the airline is in advantageous position. Later father is around to help on the books when reading PPL/CPL/IR examples. Finally, father tells HR on coffee break that his kid has got all the papers, vouches for his/her competence and asks if and interview can organized. Father tells kid what HR will asking for, what HR enjoys hearing etc.
Somewhere else, someone whose fathers parenting consisted of beating kids when drunk, worked ass off earning enough money to get the same papers. Without as much money, chooses a cheaper school with not as good teachers. Arrives to the same interview as captains kid, unprepared.
Who of the above will HR choose? Unfair? yes, life is. Nepotism? not.
Another case would be if the said airline has an AB-initio program, and "Captains kid" is chosen even thou more capable kids were interviewed.
That would be clear nepotism.
Real life, as usual, is more complex. The difference between "advantage due knowledge in family" and "nepotism" is sometimes really small.