There is no difference. Bike is just a shortened form of the word bicycle. However, as Lyss said "bike" could be a verb; to bike. I chose to bike to work. Which means that I rode my bicycle to work. But the words bike and bicycle as nouns have the same meaning.

In reference to the object, there is no difference. You can call the object a "bike" for short, or just a "bicycle". When refering to the action of riding a bicycle, it is more common to say "I will bike to ___(your destination)___" I hope this helps! :)

Bike can means any vehicle with two wheels,thus a motorcycle can call a 'bike' , a bicycle can call a 'bike'. I hope this can also claify your question.