What is a geographic feature?

A feature is a geographic object in vector data: one record with geometry (point, line, or polygon) and zero or more attributes. Features are the basic units in layers such as BGT roads, BAG buildings, or own asset points.

Via WFS you fetch features as GML or GeoJSON; in shapefiles and GeoPackage features are rows linked to geometry. Editing (split, merge, update attribute) happens per feature or selection.

A feature is not a raster cell or a whole map layer. A layer contains many features; a cell in a DEM is raster, not a vector feature in the narrow sense.