A seed keyword is a starting term you expand from: you put it into a tool or a planner and get back the queries related to it. The seeds decide the shape of everything downstream, which is why a research session that produced nothing usually failed at the first step rather than the last. Good seeds are the words your buyers use for the thing you actually sell, and there are usually fewer of them than people expect.
Where good seeds come from
Three places, in order of value. The words customers use in enquiries, support messages and sales calls, which are the only ones you know real buyers say. The queries your site already shows for, which tell you what search engines currently think you are about. And the language on the pages that outrank you, which is a reasonable proxy for what works in your subject. Brainstorming without those three is how a list ends up full of terms nobody types.
How many seeds you need
Between five and fifteen for most subjects. Fewer and the expansion is narrow enough to miss whole branches; many more and you are expanding categories rather than a subject, and the output becomes unmanageable without telling you anything new. If your seeds cover several different buyers, that is a sign you have more than one hub of work and should treat them separately.
Seeds that quietly waste the session
Terms too broad to belong to anybody, like a single industry noun, return the biggest queries in the market and nothing you can win. Terms that are your own product name return your own brand traffic, which you already have. And terms borrowed from another market's vocabulary return that market's list, which is the mistake that fills a business list with consumer queries.
What to do with the expansion
Treat everything the tool hands back as candidates rather than as a plan. Cut on relevance first, before any number is looked at, because a large volume attached to a query your page cannot satisfy is a trap rather than an opportunity. Then score what survives on your own figures.
Questions people ask about seed keyword
What is a seed keyword?
A starting term you expand from to generate a candidate list. The seeds you pick determine what the whole list can contain.
How many seed keywords should I use?
Usually five to fifteen. Enough to cover the branches of one subject, few enough that the output stays readable.
Where do I find good seeds?
Customer language from enquiries and support, the queries your site already gets impressions for, and the vocabulary of the pages that currently outrank you.
Should my product name be a seed?
No. It returns brand traffic you already receive and crowds out the queries from people who do not know you exist yet.