Glossary
Period & cycle terms, in plain words
Cycle tracking uses a lot of jargon. This glossary defines the fourteen terms you'll meet in Mori and in other trackers — what they mean biologically, and what they mean inside the app. Nothing here is medical advice; it's vocabulary so the numbers on your calendar make sense.
The basics
Period
The bleeding days at the start of a cycle. In Mori a period is a range — you mark each day it lasts, and the app groups consecutive days into one event automatically.
Menstrual cycle
The span from the first day of one period to the day before the next period starts. If your period begins March 1 and the next begins March 29, that cycle was 28 days long.
Cycle day
Where a date sits inside a cycle, counted from day 1 = the first day of the current or most recent period. Cycle day 14 in a 28-day cycle is mid-cycle; the same day 14 in a 35-day cycle is still early.
Cycle length
How many days a completed cycle lasted. Anywhere between roughly 21 and 35 days is common. Mori learns your personal range from your records instead of assuming a default 28.
Period length
How many days bleeding lasts within one period — often 3 to 7 days. Mori uses your average period length to project the end of an estimated period, not just its start.
Phases
Follicular phase
The first half of the cycle, from the first period day until ovulation. Its length varies the most between cycles and between people — it's the main reason cycle lengths differ.
Luteal phase
The second half of the cycle, from ovulation until the next period. It's more stable — usually around 12–14 days — which is why back-counting from an expected period is the usual way to estimate when ovulation happened.
Ovulation
The one-time release of an egg per cycle. No calendar app can observe ovulation directly — it can only estimate a likely day from your history. Mori labels it as an estimate, always.
Fertile window
The days when pregnancy is most likely: roughly the five days before ovulation plus ovulation day itself, because sperm can survive several days while the egg lives about one. It's an estimate, not a contraceptive tool.
Prediction terms — what Mori's numbers mean
Estimated period
The date range Mori shows for your next period, computed from your own past cycles. It's a projection from your data — not a medical measurement.
Prediction range
The earliest-to-latest span of an estimated period. A narrow range means your recent cycles were consistent; a wide one means they weren't, or there's little history to go on.
Confidence level
How much your history backs an estimate. More recorded cycles and steadier lengths raise it; sparse or irregular data lowers it. Mori shows it so you know how much to trust the number.
Cycle regularity
How consistent your cycle lengths are. Stable cycles → tighter ranges and higher confidence. Variable cycles → honest wider ranges instead of a fake-precise date.
Cycle cluster
How Mori groups your logged days. Five consecutive marked days are one period, not five separate events — so statistics and predictions count it once.
How these terms appear in Mori
The cycle ring shows your current cycle day and today's phase. The calendar marks logged period days, the estimated period range, and the estimated fertile window — each visually distinct, and predictions never cover up real records. The prediction card states its basis and confidence in words, so you can always see why a range is wide or narrow.