Creeping Jenny, Creeping Charley,
Two totally different things - although often confused. Creeping Charley is a weed (also known as ground ivy) that was probably introduced as a shade loving ground cover at one point or another... like most invasive species, we seem to be the reason they all get where they shouldn't! It's nearly impossible to control without resorting to herbicides or digging out whole areas of your lawn. Ask me how I know...
Anyway... creeping JENNY is a moneywort. Also an aggressive grower, but easy to contain with a little effort. Look for the golden or yellow variety if you're new to creeping Jenny - it's a bit less aggressive, although still impressive in it's ability to spread! In the sun it's full on yellow; in shadier areas it's more chartreuse-y green.