A search result format beyond a conventional text listing, such as a featured snippet, local pack, image result, or knowledge panel.
SERP feature is an industry umbrella term for a search-results presentation beyond a conventional text listing. A feature might emphasize a quick answer, a collection of images, business information or another useful format. Naming the feature matters because different presentations are selected and assembled in different ways.
Do not assume every feature is a rich result produced by structured data. Google documents multiple visual elements and separate requirements for supported structured-data enhancements. Adding markup can make an eligible page easier for a system to interpret, but it does not purchase or guarantee a special display.
For planning, begin with the information the feature is meant to help someone find. If your page is a good source for that information, review the relevant requirements and the accuracy of the underlying content. Avoid adding unrelated markup merely because a competitor has a more prominent result. A feature that answers a question on the results page also should not be treated as a guaranteed visit to your website.
Takeaway: Identify the specific result feature before asking for an optimization change. The right work depends on the feature, your page’s purpose and the information you can accurately provide.
Example
A retailer notices product information in some search results and asks its developer for “more schema.” A better brief identifies the relevant product pages, checks whether their visible price and availability are accurate, and reviews the applicable product requirements. The feature being considered determines the work; a generic markup package does not.
What to check
Use the search engine’s documentation for the exact feature. Keep expectations separate: technically valid markup, eligibility, actual display and customer action are different things. Record what you observe without promising that a particular presentation will persist.
For more detail, see Visual Elements gallery of Google Search.