Virginia creeper. It has heart-shaped dicotyledons, then the first "true leaves" may have 3 leaflets rather than 5 -- looking much like poison ivy. [The heart-shaped dicotyledons show it's safe, as PI has dicotyledons which are long ovals.]

Thank you! I wonder if this is what is in my backyard, too. I have been told it is poison ivy, but no one seems to be having any trouble with it. I will yank this one in the front and look at the back. :)

With Virginia creeper, it's only the first couple of leaves which may have less than 5 leaflets.

Ah, ok. Thanks!