Historical is a popular genre of anime and manga that portrays works set in past time periods. A historical series could be set in a vague or general era such as Sengoku time period or 1940s, or even vague and unspecified points in history.
The historical setting is usually more realistic, featuring elements and settings more true to the time period it takes place like Rurouni Kenshin and Golden Kamuy. It often can feature fantasy or supernatural elements as magic, demon hunting, etc, like Kimetsu no Yaiba or Baccano. The time period could also be alternative history and feature unusual technology and weaponry for its time.