legitimate would mean it was caught be normal game play no rng manipulation, no glitches, no bot abuse, nothing but gameplay as intended.
if u want ill copy the definitions the hackcheck staff uses, since u dont understand how to i guess.
Hacking and Genning Terminology
Hacked - Generally refers to Pokémon that were illegally added to the game with third party software. These Pokémon cannot be obtained by any other means.
Generated/Genned - Generally refers to Pokémon that were illegally generated in game with third party software. These Pokémon often look legitimate, and can be obtained by other means.
Legitimate - The Pokémon was obtained via natural gameplay, without modifying how the game generates Pokémon in any way.
Illegitimate - The Pokémon was obtained outside of normal gameplay. This could mean the Pokémon was obtained via glitches, RNG abuse or bots.
Legal - The Pokémon has values that could exist naturally through normal gameplay, regardless of whether it was actually obtained through normal gameplay and regardless of how unlikely the Pokémon is naturally.
Illegal - The Pokémon has at least one aspect obtained through intentional glitch/cheat usage, and could never occur naturally.