As I understand mesons in most sci fi sense its a mass of quarks and anti-quarks (as real mesons are a pairing of the two) that phase in and out of existence as they travel. So it would be timed so when going through the shields and armor of a ship its phasing but when it is going through the interior component it is in a phase that is the same as the reality we live in and therefore able to interact with it. My very limited understanding of actual mesons says this explanation is not, strictly speaking, impossible just out of our current grasp. But that is off topic.
Not quite. In the real world, as you say, a meson is an unstable particle composed of a quark and an anti-quark. Because it's unstable, it has a finite life-time (very similar to a radioactive half-life) which indicates the time it takes to undergo total matter-anti-matter annihilation (I love saying "total matter-anti-matter annihilation") and turns into other particles like photons. The technobabble is that you speed the mesons up to close to the speed of light so that the relativistic time dilation factor keeps them alive long enough to travel into the other ship, where they decay. If they're neutral mesons like pi0 they'll only interact with the armor using the strong force (not electro-magnetism) so they'll slide right through and decay inside the other ship. IIRC this is the technobabble from Traveler, which I think is where Steve
lifted borrowed them from. No phasing in and out of reality - just time dilation. In reality there are a bunch of problems with the idea, like the fact that the lifetime is more like a half-life (so they'd be decaying all the way to the target), their lifetimes are very short so you'd need a REALLY high time dilation factor, the difficulty of making mesons without banging a particle beam into a target on your own ship (and vaporizing it) and the difficulty of steering/accelerating uncharged particles. Buy hey, that's why it's called technobabble
John