Thus far, I've only considered slice of life to be a genre of anime. Everyday life, full of shenanigans and all that. But now, I get the feeling it can also be part of a writing style. I'd appreciate it if someone could clear up my confusion on the subject.
I'm not an expert in these things, but my personal impression of slice of life is a bit different from the above poster. Maybe I'm just completely off though.
Anyway, I feel that slice of life follows a character/characters through a period of their life. It doesn't have to detail their daily life or whatever else, but the main theme of the story is how this period of time affected/changed the character/characters.
Say for example, a story where a zombie apocalypse happens, and the story is about how they save the world.
If your focus for that story is on the world and how it is being saved, that's not slice of life.
But if your focus is on how the protagonist grows, and slowly changes throughout the events, and "saving the world" is just a minor plot point within the story to show the character growth, then it is a slice of life.