What is the piece that holds the pant legs together called? Is there an "official1" name? Or is there just a commonly agreed on term?
1Official meaning something mentioned, even in passing, by Lego in some way.
They are referred to as "Minifig Hips" almost everywhere: [partlink:970:4].
The LEGO Pick-a-brick service doesn't sell them without legs, and just refers to the whole construction as "Mini Figure Mini Lower Part":