Profession: What do you do?

Our Career.  It is how we earn our income & make a living.  In a fantasy world, this is a little harder to seperate.

Adventurers go on quests, defeat horrors.
In city environments, characters can be consultants, laborers, or complete other tasks.

Life doesn't stop when you get back to town.  What characters do in the tavern or town has impact on the area & region.  Often whatever the NPC, villians, or monsters are doing in the area affects the character & its residents.

It is overlooked in every game system.  To me, this is part of the character's background & purpose.
For example, if you are an accountant, you are likely also organized & methodical.  These skills are part of how you approach problems in life & what you do.  Ignoring this insight is too limiting.  It is also a subset of your total background.  Maybe you like to rebel with friends at night, but enjoy the structure of your accounting job during the day (for example).  This trait is part of your background, but not part of your profession.  This is why it is important to distinguish the two.