There's "invasive" in terms of "ability to identify you, times ease of capture." Irises (and maybe faces) are very invasive by this metric.
Or there's "invasive" in terms of how much cooperation it requires to match you. I think that's what parent meant. A biopsy DNA sample or interrogation would be most invasive, followed by maybe something like a cheek swab, then palmprint, then willing fingerprint (ignoring latent fingerprints), then iris, then faces being the least invasive.
