Describing a sequence of numbers generated by a deterministic computer that is seemingly random, but eventually repeats. Good pseudo-random number generators have very long periods before the sequence repeats.
The date Easter falls on is pseudo-random in that it cannot be predicted off the top of someone's head, and it takes 5.7 million years for the sequence to repeat.

To generate a pseudo-random number in C, you'd use the Rand(); function.
Get the pseudo-random mug.
A set of numbers that seem random but actually aren't. They are predetermined by a computer algorithm that is explicitly designed to generate the most random of the random, if that makes any sense.

The problem with true random is that numbers will often repeat themselves, which to our usage is not ideal. Pseudo-random number generators fixes all that.

So ironically, the most random RNG is actually not at all random.
You'd use a pseudo-random number generator for dice
Get the Pseudo-random mug.