Does the level of risk vary according to the term of the bond? Which term is generally speaking more or less risky and why? Vanguard's long term bond index had the highest returns (and yield). Doesn't that also mean it has the highest risk?

Are fed govt bonds generally less risky than corporate and municipal bonds?

Does anyone have experience with these Vanguard funds? I don't but I suspect others might. Also Vanguard has a lot of bond funds, IIRC.

What's IIRC?

Some bonds are insured so that the holder is protected to some degree though this does come at a cost somewhere.

Is there a special name for an insured bond or would I just have to plow through the prospectus to find out?

Thanks for your very thorough reply!!
CMW