Just a week or so after the CyanogenMod ROM team expanded its support for LG's Optimus G flagship, another high-end smartphone has been added to the mix. The Optimus 4X HD (also known as the P880) just showed up on the official CyanogenMod servers, in a 10.1 (Android 4.2) build no less. Right now there are only two builds posted, but that should increase fairly quickly, and the Tegra 3 internals mean that the CyanogenMod developers will be on familiar ground.
Definition: A "nightly" is a bleeding edge release that is built on a daily basis, usually at night after a full day's worth of new code has been committed.
It could oftentimes be unstable and not properly tested, lacking any changelogs, but eventually evolving into alphas, betas, release candidates, and finally stable releases.
If you're a bit confused, recall that the 4X HD was LG's flagship for the first half of 2012, roughly comparable to the HTC One X. While LG's smartphone marketshare isn't much outside of Asia, and the phone never got a carrier-supported release in the US, it was well-received by those who used it (including our own David Ruddock).
The usual warnings apply: those who aren't comfortable with the bleeding edge of custom ROMs shouldn't install nightlies, and those who enjoy seeing all their apps and settings disappear should refrain from backing up in the custom recovery of your choice. As with all CyanogenMod ROMs, you'll need Gapps if you want access to the Play Store and Google services.