Keyword weight
How much a keyword counts for your product: its monthly searches times how relevant it is to products like yours.
Every keyword of a product counts by what it is really worth to you. Two things decide that. First, how often shoppers search for it each month, from Amazon's own search data. Second, how relevant it is: how much of the top 10 organic results are products like yours, with higher places counting more (your listing, your competitors and other products of the same type). A big keyword whose top results are other products counts little; a smaller keyword whose top results are products like yours counts a lot. Relevance is measured again with every capture, so the weights follow the search results. Keywords too small for Amazon's search data count with a small fixed number of searches. A keyword you add yourself counts like a typical keyword of your product until its first capture.