A groundcover plant is exactly what it sounds like- a plant that grows low, and spreads out over a large area. Most people have grass as their groundcover in their yards- because it just automatically grows and is easy to manage. However, there are so many more options out there! Check out this post by Joy at Bless My Weeds for what to plant with your grass:
-Thyme- has a beautiful scent and purple flowers
-Golden Moneywort- This groundcover grows really well in most climates and spreads rather quickly. It also is a classy gold color.
-Lamium- extremely easy to grow, grows pink and white flowers
-Sweet Woodruff- low maintenance and non-invasive.