One list, two jobs
Keyword research is easy to mistake for an advertising task, or for a listing task, and it is neither on its own. It is the layer both depend on. The terms a buyer types to find a product are the same terms the listing has to rank for organically and the same terms the campaigns bid on. One ranked list feeds both surfaces.
That shared dependency is why this stage sits where it does. You have already chosen a product and studied the market it competes in. Before writing a word of listing copy or opening a single campaign, you turn that market into the vocabulary buyers actually use. Skip it, and the listing and the ads end up chasing different words.
Relevance beats volume
The most tempting mistake is to sort by search volume and work down from the top. A high-volume term looks like opportunity, but volume only matters when the traffic it brings is traffic you can convert. A broad term that draws shoppers looking for a different product will cost you either way: in ads, you pay for clicks that do not buy; in the listing, you dilute the relevance signals that decide organic rank.
Relevance comes first. Judge each candidate by how closely it matches what your product is and who it is for, then let volume break ties among the terms that pass. A smaller, tightly relevant term usually earns its place. A large, loosely relevant one rarely does.
A term you cannot convert is a liability
High-volume traffic you cannot win drains ad budget and weakens the listing it should have strengthened.
The master keyword list
The artifact this stage produces is a single master keyword list: every term worth targeting, scored and ranked, in one place. It is the reference the later stages read from rather than a document you write once and forget.
A finished list has recognizable properties: