What does it really mean for something to be "trivial"? I see this word a lot when I read about mathematics. Is this meant to be another way of saying "obvious" or "easy"? What if it's actually wrong? It's like when I see "the rest is left as an exercise to the reader", it feels like a bit of a cop-out. What does this all really mean in the math communities? 

It can mean different things. For example:
Obvious after a few moments thought.
Clear from a commonly used argument or a short one line proof.
However, it is often also used to mean the most simple example of something. For example, a trivial group is the group of one element. A trivial vector space is the space {0}. 
