When did the new season of flash start?
No context provided
When did season 3 of The Flash start?
October 4, 2016
No context provided
When did season 4 of The Flash start?
October 10, 2017
No context provided
When does season 5 of The Flash start?
October 9, 2018
The Flash (2014 TV series)
https://en.wikipedia.org/wiki/The%20Flash%20%282014%20TV%20series%29
The first episode of the season premiered on The CW on October 4, 2016, and was watched by 3.17 million people, with the season consisting of 23 episodes.
The Flash (season 3)
The fourth season of the American television series The Flash, which is based on the DC Comics character Barry Allen / Flash, premiered on The CW on October 10, 2017, and ran for 23 episodes until May 22, 2018. 
The Flash (season 4)
The fifth season of the American television series The Flash, which is based on the DC Comics character Barry Allen / Flash, premiered on The CW on October 9, 2018, and concluded on May 14, 2019, with a total of 22 episodes.
The Flash (season 5)
The Flash has various seasons. The third season was premiered on The CW on October 4, 2016. The fourth season was premiered on The CW on October 10, 2017 while the fifth season was premiered on The CW on October 9, 2018.