You can obtain KVIrc in three ways:
The official packages are released least frequently but are the most stable ones. Each official source package is well tested and will probably compile on your system. You also have more possibilities to find a binary package suitable for your system. The on-line FAQs and documentation refer to this type of package.
The Git development snapshots are unofficial packages extracted from the Git on a continuous basis. Each snapshot reflects the Git state on a particular revision and you're likely to find a really recent one. The packages have been tested on at least a couple of systems and have a good possibility to compile on yours. There are also some binary builds available.
The latest bleeding-edge sources can be downloaded by using the Git system. We're trying to keep the Git as "clean" as possible but finally the sources are not guaranteed to compile. Currently there are Git development snapshot builds, see KVIrc's Github project page for details on this.