Cycle begins from the first day of the period and ends on the day before the next period. Typical cycle last 21 to 35 days with an avg. of 28 days.
Period length refers to the number of days from the beginning to the end of the period. Typical period last 2 to 8 days with an avg. of 5 days[1].
Your fertile window refers to the most fertile days in your cycle. Although the length of the fertile window varies between all women, but it usually last for 6 days and the ovulation occurs on day 6 [2].
If you have a regular cycle, ovulation will take place around 14 days before your next period [3].
The days other than period and fertile window are theoretically safe period, but contraceptive measures are still needed.
[1] The Office of Women's Health
[2] US National Library of Medicine
[3] Stanford Children’s Health