In 22 years, there have been 1,648 talks and panels at DEF CON, all of which may be found in the DEF CON Archives. The very first presentation listed is Ray Kaplan’s “To Hack or Not to Hack, That Is Not The Question”, and the last is Zoz’s “Don't Fuck It Up!”.
I copied all of the presentation names, then sorted and subtotaled the individual words in a spreadsheet. There were more than 11K words overall, of which about 3.5K were unique, ranging from “abuse” to “zombie”. Finally, I dropped all of them into a free online “tag” or word cloud generator.
As you can see, the most frequent word used at DEF CON is “hacking” (128), followed by “security” (122). The logic is clear. Enjoy.