This is the 770th most frequent German word.
frank
The German word "frank" does not exist; you may mean the English word "frank" or a similar German word like "frankieren" (to affix postage).
In this sentence, "frank" is used as an adjective to mean honest and direct in expressing opinions.
Er war sehr frank und sagte direkt, was er dachte.
He was very frank and said directly what he thought.
In this example, "frank" is used again as an adjective to describe someone's candid behavior.
Sie war bekannt für ihre offene und franke Art.
She was known for her open and frank nature.
Here, "frank" could hypothetically be used as a noun (although this is not common in standard German), referring abstractly to someone or something exemplifying frankness.