Specifically in electronics there are actually milspec versions of some microchips, different from the consumer grade ones (they have a wider range of operating temperatures plus I also believe higher resistence to electromagnetic radiation and mechanical vibration, similar to microchips “for automobile automotive use”), but I suspect that when it comes to actual consumer electronics devices the words “military grade” are not a protected tag (as in, electronic devices said to be “military grade” are not forced by regulation to have certain characteristics) so those words are generally marketing bullshit.