snakecase lowercases everything and joins words with underscores: pageloadtime, metadescription, total_clicks.
Where it is standard
Python variables and functions, Ruby, SQL column and table names, many configuration formats, and a large share of REST API field names.
Why underscores rather than nothing
Words stay visually separate without relying on capitalisation, so the name survives systems that lowercase everything — which SQL identifiers frequently do.
The related conventions
kebab-case uses hyphens and appears in URLs and CSS. The distinction matters because a hyphen is not valid in identifiers in most languages, while an underscore is.
Try it: Convert to snake_case on SeoWolf's Notepad.