looks like a spirea..

Just googled spirea and I think you're right! I'm glad to know it's not just an overgrown weed specimen. Thank you!

now is not the time but if it's out of shape they respond well to pruning..

Thanks! It does need to be pruned - it's growing all over and there seem to be suckers popping up several feet away. I am not sure I want it in its current location anyway, but I'll wait till spring, prune it back hard and see what I think.

Don't prune it back until after it has flowered. If you do it before you'll lose next season's bloom.

I defer to Embo's knowledge of this particular Spiraea.

Since it looks to be one on the order of Spiraea japonica probably you can get away with cutting the whole thing off at 4 to 5 in. above the ground at the end of winter and still have it flower the same year. There is some variation with species but generally the genus separates into two groups: those which flower on branches formed the year before and those that flower on new growth. It is the first type that will not flower the following year if all mature growth is removed.

Good to know. If I decide I want to move it to a new location, is end of winter/early spring a good time to dig it up and transplant? Is transplantation even possible with something this well-established? I know you can't see the base of the plant from my photos but it's fairly large, with suckers covering at least a 2-3 square foot area.