I hate to be Professor Pinhead of the Kollege of Musical Knowledge but here's my "theory":
1) Jangle is 1965 - post beat, pre garage / psyche, and contemporaneously coexistent and sharing common vibes with surf and electrified folk.
2) Jangle is NOT fuzz, grunge, air guitar hero, ballady, classic rockish, sludge. Jangle is the Anti Classic Rock.
3) Jangle is bright, chimey, two / three string chord based, toggling majors / minors with lots of scratched upstroke. No power chords or similar deviations. And just enough treble and soft distortion to give it a third dimension. The Edge could have been a great jangle guitarist had he so chosen that path. Alas ... he did not. Maybe Rickenbacker and Twelve String fall into the definition somewhere. Dunno. Don't want to overthink it.
4) Jangle is a steady driving cantering tempo - with awesome understated bridges. Jangle is not dark, evil, degenerate, quirky, etc. etc. etc. It's just jangle - it's one of those German words that sound like what they mean.
IMHO of course - and I myself stretch the boundaries into surf and psyche - but I avoid garage cuz that's a totally different animal. Whew! I could sure use a refreshing Cup of Jangle ...
.