This plant, also known as Yellow Wood Sorrel, is a common plant of yards. It’s a cute little guy with trifoliate, heart-shaped leaves. They remind you of clover, but aren’t closely related.
The taxonomy of this and other similar plants is quite complicated. In fact, there are 24 alternate scientific names for this plant, which means that its scientific name has changed 24 times since the beginning. It’s probably not worth trying to identify every plant down to the species, since you never know when that will change. I just call them all Wood Sorrel and am happy with that.