Understanding 1080-60i (1920x1080, 29.970 fps)

Hi - probably a dumb question here, but every time I think I start to get a handle on frame rates, aspect ratios, "i" vs "p" etc., something comes up that throws me off.

I've read a lot about rendering "1080-60i (1920x1080, 29.970 fps)" - but my question is this ... is it "i" or "p" ... is it 60 fps or 29.97 fps? How can it be both in the same settings?

Like I said - p'bly a dumb question ... but ....

TIA!

KenM
Sound Works R&P