Border plants are those which edge a garden bed or space. Small plants that define the extent of the garden bed or delineates paths.
Borders give structure and formality to the garden, saying the grass ends here and the garden/path starts there!
Generally, these will be low growing plants that allow a view to the rest of the garden, maybe less than 300mm high, perhaps even ground covers. Plants may be neatly trimmed in formal landscaping or left as leafy grasses where a softer look is desired.
Informal gardens will use plants that don’t require frequent clipping; Liriope ‘Evergreen Giant’ make excellent border plants and may be placed in a single line or two or even morphed out in irregular shapes.
Borders may extend some distance and either be exposed to sunlight or shade. In this case, you may want a plant species that is tolerant of both regimes or elect to change the species part way down the length according to suitability.