Needs a source
According to an article on animenewnetwork, Media Factory announced that High School DXD season 4 will be called High School DXD Hero at a panel during Fantasia Bunko festival,.
Along with the titled announcement a new visual and trailer were screened. You can watch the trailer below.
The new season will be released in some time in 2018.
If you haven’t heard of High School DXD before, here is a synopsis from the trailer’s description: After being killed by a fallen angel, Issei Hyodo is brought back to life by the gorgeous president of his high school’s Occult Research Club, Rias Gremory, who turns out to be a high-ranking demon. With devilish new powers, Issei is bound to serve Rias for the rest of his life.
If you are interested in watching High School DXD or would like to get a refresher before the new season releases next year, please visit Hulu.