How drop rate works?

Hi there.

I wondered how the drop rate works and what it means (?)
Let's say I try to farm for The Last Flame with a 0,5% drop rate. What does that 0,5% mean?
A) Does it drop at average every 200 boss kills?
B) Every unique relic that drops from the boss has a 0,5% chance to be The Last Flame?
C) Every Incense Relic that drops from the boss has a 0,5% chance to be The Last Flame?

Here is some data for 33 runs. 0 Last Flame
https://www.reddit.com/r/PathOfExile2/comments/1i078hn/trials_of_sekhemas_unique_relic_drop_data_and/

44 runs
https://www.reddit.com/r/PathOfExile2/comments/1ibwhal/going_for_last_flame_relic_will_be_keeping_track/

Huge sample size (See comments aswell)
https://www.reddit.com/r/PathOfExile2/comments/1im4iyd/i_have_seen_a_total_of_300_unique_relics_dropped/

It only drops from Zarokh.
https://poe2db.tw/us/The_Last_Flame

Cant confidently say the drop rate.

Here is a reddit post about increasing your odds (See first comment)
https://www.reddit.com/r/PathOfExile2/comments/1if8sjo/living_my_most_legendary_gamer_moment_515hrs_in/