They're similar, but typically if you are just shy you may just need to warm up, whereas an introvert constantly craves solitude or a limited amount of people. (This is only one view on it, for there may be many differences or reasons behind this.)

Extrovert = enjoys being around people
introvert = enjoys being in solitude

I'd say they are similar but introvert is more of a lifestyle

I'm an introvert due to childhood trauma and rejection. Therefore, I believe it had been a conditioning which contributed to my 'hard wiring'. I am shy(to have reserve) due to the dread of rejection. I am an introvert due to choosing who to talk to...not very many people are interesting to me in my city, they have predictable thoughts and behavior..they are religious. So why do I live here? Because it is beautiful - forest, forest animals, clean air, affordable, very rare to have crime, and it's not odd to see people walking-not using cars.

There are behaviors associated with being an introvert that may not be attributable to just a shy person. But it is not black and white. No hard and fast rules here

Not much difference to me, although it gives extroverts a way out of being boring, "oh, he/she is just shy".

I'm an introvert and sometimes I feel shy, however, sometimes I'm full of confidence and can take on the world. So I think they may be two different things.

Nothing is black and white, but as a generalization, I think shy is fear and being an introvert is preferring your own company.