What is the difference between flute and concert flute?

There is no difference between flute and concert flute. The term "concert flute" is sometimes used to refer to the standard transverse flute, which is the most common type of flute used in Western classical music. However, the term "flute" can also be used to refer to any of the various types of flutes that exist, such as the piccolo, alto flute, bass flute, and so on.