Textual relevance measures how well a document matches a query. However, since not all fields in a document are equally important, the relevance of each individual field can be adjusted.
Field boosts allow for fine-tuning how much weight a match for a given field contributes to the overall index score. Unless a field has a field boost assigned, it won't be searched.
Weighting is relative. "0.2" is twice as important as "0.1". "0.4" twice as important as "0.2" and so on.
Assuming a product has three fields and the following scores assigned to them.
A keyword match in the title field has the highest weight, where a match in the category field is considered less important. However, if your customers tend to search for categories rather than specific products, increasing the score for the category field is likely to improve the search results.
Tip: Score fields by importance to your business. Aim to have few fields with scores above 0.5 to avoid over-saturation. When everything is important, nothing is.
Minimum index score
The minimum index score determines which products should be included in the search result set. Products with an index score lower than the minimum index score are not be included.
Assuming a search for "watch". The top results match the keyword watch in the title or other high scoring fields like category. Due to it being a perfect match the resulting index score is "1". Accessories, like wrist straps, are likely to mention the term "watch" in the description. But due to the lower score assigned to the description field, they have a lower overall index score. This could be a "0.4" for example.
The minimum index score enables you to decide whether you want those lower scoring results included in the search results are not. If set to "0.6", none of the accessories that scored lower than 0.6 are included in the results. if set to "0.4", they would be shown.
Tip: Whether it makes sense to surface lower scoring results depends on your requirements. We recommend experimenting with different scores to identify what setting yields the best conversion rate for your business.