[vl]

But isn’t it just “two phase”? I.e. how “true” two phase would be different?

Ok, help from our new common friend:

Yes, your statement is essentially correct. In the United States, residential electrical supply is typically a single-phase, 240-volt system that is "split" into two 120-volt legs. Each of these legs are 180 degrees out of phase with each other, which allows for both 120-volt and 240-volt circuits within the home. This arrangement is often referred to as "split-phase" electricity. It's not technically two-phase because a true two-phase system would have two waves offset by 90 degrees, not 180.