Being out of the ordinary. Not bound by or in accordance with convention : Different from what is usual or from the way most people do things:
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Not following what is done or considered normal or acceptable. The meaning of unconventional is not conventional : Unorthodox, original, unusual, irregular, atypical, different, uncustomary the vaccine had been produced by an unconventional technique.
Definition of unconventional adjective from the oxford advanced learner's dictionary.
If you describe a person or their attitude or behaviour as unconventional, you mean that they do not behave in the same way as most other people in.