The overflowing scroll state query, whose values are none | top | right | bottom | left | block-start | inline-start | block-end | inline-end , is described as

The overflowing container feature queries whether a scroll container has clipped scrollable overflow rectangle content in the given direction which is reachable through user initiated scrolling. That is, overflowing does not match for a hidden container, nor for a negative scrollable overflow region.

But colloquially, content that overflows and is clipped is still considered overflowing.

If the question is, "can I scroll in this direction", perhaps a better name would be scrollable?