Absurdist fiction is a genre where the action does not need to follow a sequential order, neither does the plot need to begin and end. The characters do not have to be concise, nor represent anything nor anyone. The theme in an absurdist fiction is mentioned, elaborated, but not sequentially worked. It is most commonly seen in theatre and poetry rather than plain narrative, but it is also found there.
If you see any theatrical piece of absurdity what you will find is maybe a character which starts saying something and may not end it, then the action quickly switching to another time and place, and maybe even other characters showing up and similarly disappearing throughout the action for no real reason. In other words, it is very similar to those Obsession commercials from back in the 80s.
Absurd realism is also an existentialist-based genre. It also abandons most rules of traditional storytelling in that the characters may use free dialogue, themes might not be fully explained, and there may or may not be a "lesson to be learned". The thing with this one is that sometimes there might be a realistic central theme, but all that occurs around it is quite, well, absurd. The actions that take place are not as wild as with absurdist fiction, but also follow a trend of weirdness. An example of absurdist realism is said to be the story Catch 22.
The link provided might be of some help to you.
This was a hard one- hope it is of some help.