> You call it "BS" for some reason (you seem not to believe in it)

The balance sheet is typically abbreviated as BS, so a BS account is a balance sheet account.

It's been a while since I've had anything to do with goodwill, but if I remember correctly it's most commonly the difference in the assets net market value and the purchase price of a company. So if company A buys company B, which has assets of $50 for $100, then they'll add $50 in goodwill to account for the difference.

This is, of course, a simplification as I'm sure goodwill is regulated under GAAP/IFRS. But it does mean that you can't use goodwill to accurately estimate the effects of brand advertising as there could reasons other than brand marketing for a company being traded above its assets' fair market value at the time of the sale.