1. Unpredictable (closest to mathematical definition); weird. “The system's been behaving pretty randomly.”
2. Assorted; undistinguished. “Who was at the conference?” “Just a bunch of random business types.”
3. (pejorative) Frivolous; unproductive; undirected. “He's just a random loser.”
4. Incoherent or inelegant; poorly chosen; not well organized. “The program has a random set of misfeatures.” “That's a random name for that function.” “Well, all the names were chosen pretty randomly.”
5. In no particular order, though deterministic. “The I/O channels are in a pool, and when a file is opened one is chosen randomly.”
6. Arbitrary. “It generates a random name for the scratch file.”
7. Gratuitously wrong, i.e., poorly done and for no good apparent reason. For example, a program that handles file name defaulting in a particularly useless way, or an assembler routine that could easily have been coded using only three registers, but redundantly uses seven for values with non-overlapping lifetimes, so that no one else can invoke it without first saving four extra registers. What randomness!
8. n. A random hacker; used particularly of high-school students who soak up computer time and generally get in the way.
9. n. Anyone who is not a hacker (or, sometimes, anyone not known to the hacker speaking); the noun form of sense 2. “I went to the talk, but the audience was full of randoms asking bogus questions”.
10. n. (occasional MIT usage) One who lives at Random Hall. See also J. Random, some random X.
11. [UK] Conversationally, a non sequitur or something similarly out-of-the-blue. As in: “Stop being so random!” This sense equates to ‘hatstand’, taken from the Viz comic character “Roger Irrelevant - He's completely Hatstand.”