What is the difference between cv,resume and bio data?

CVs are in the UK. Résumés are in the US.
Biodata is in South Asia.

They’re all the same thing.

In Australia, the terms ‘CV’ and ‘Résumé’ are used synonymously, amongst my generation, anyway. Prior to that, the terms were somewhat related, a CV simply being a much more detailed résumé.

In the US, CV is used as the term for extended resumes for people working in academia, like professors and so on, and mentions their published work as well as their other credentials.

In the US CV is used by medical professionals and people in academia as some have already mentioned. I disagree that a CV is a more detailed resume, the words are synonomous in my mind. Most countries use CV I think for all “resumes,” I think the US is the unusual one. CV, which stands for Curriculum Vitae is the Latin, so it kind of makes sense that science and medicine use CV since they use Latin quite often.

Maybe my understanding is baseless, but I do see a difference. I think of a resume as being explicitly oriented toward job-seeking, whereas a CV is more of a historical document—just a description (in brief, typically in list form) of a person’s background and career. I would hand in a resume if I were applying for work, whereas if I were a speaker at an event I might supply a CV from which the person introducing me would draw relevant particulars.

My CV would not change over time except to have additions (the past would not change). But I might create a different resume for different types of job applications, varying the emphasis and the amount of detail according to the type of position sought.

A CV would be more useful than a resume in writing an obituary.

I agree with @Jeruba. A resume is career oriented, and might change depending upon the position sought. A CV is achievement oriented, and would be seen perhaps at a symposium, or other type of academic gathering. Biodata is what you might see in an artist’s portfolio.