We speak of deliberate dishonesty when there is a premeditated act of fraud that may include forged or fabricated data, falsified or invented results, plagiarism, etcetera. The scientist in question has, intentionally, ignored the rules for good scientific practice. He or she is not following the moral rules of science. Trust is undermined, which can have dire consequences both in the field of research and in the public eye.
For a student’s perspective on deliberate dishonesty, take a look at the video below.