In my vocabulary, that term means scientifically plausible or at the very least not manifestly impossible. But core elements of Three Body are just that: impossible. Even without going into the bizarre dimensional unfolding of protons (which are not even fundamental particles) to nice 2D membranes on which circuits are etched using meson beams (...), the resulting sophons are then used to communicate instantaneously over interstellar distances, courtesy of quantum entanglement. And no, that's not how quantum entanglement works; you can't use it to transfer information at superluminal speeds.
The "science" in Three Body is at the level of Star Trek technobabble. It might sound sciency to laymen, but it is really just magic with a modern coat of paint.