Iambic Tetrameter - does it pertain to poems? Or to lines?

I’m reading a poem in which the odd lines use iambic tetrameter but the even lines have only seven syllables. Each verse has four lines of 8,7,8,7.

Something like this:

De dum, de dum, de dum, de dum,   <— 8 syllables
De dum, de dum, de DUM DUM        <— 7 syllables

My question is in two parts.

1. When we talk of iambic tetrameter, can the phrase refer to a particular line or does it necessarily refer to the whole verse or even poem?
2. Would it be inaccurate to refer to this poem as in iambic tetrameter? Is there a better name for this rhythm?

Thanks!