Glossary

Glossary

Terms used precisely throughout the wiki. Where a word has a loose everyday meaning and a narrow one here, the narrow one is what the pages mean.

Adjuster. A function that moves a date to a related date by a rule rather than by a count: next_weekday, nth_weekday_of_month, date_from_iso_week. Named for java.time's TemporalAdjusters.

Ambiguous time. A local time that happened twice, because a fall-back transition repeated it. Ask Zone.is_ambiguous. See also overlap.

Business day. A day the market is open, used specifically in the ISDA sense of rolling a date that lands on a closed day. Governed by BusinessDay. Not interchangeable with weekday.

Civil time. What a clock on a wall reads: year, month, day, hour, minute. It says nothing on its own about which instant it refers to until you supply an offset or a zone. Contrast instant.

Constrain. The Overflow mode that clamps a date past the end of a month to the last valid day, so 31 January plus one month is 28 or 29 February. The default, and java.time's behaviour.

Day count. The convention that decides the denominator of a rate or the tau of an option price: ACT/365F, ACT/360, ACT/ACT ISDA, 30/360, 30E/360, ACT/252. Per the ISDA 2006 Definitions.

Early close. A scheduled short session, not a closure. The market trades. is_early_close returns false on a day the market is shut, because a closed market is not an early close.

Envelope. A session's whole window including any break inside it. bounds() returns the envelope; break_bounds() returns the hole.

Exact time. Arithmetic on instants, measured in milliseconds. Contrast civil time. The plus_ms family, not the plus_days family.

Gap. A local time that never happened, because a spring-forward transition skipped it. Ask Zone.is_gap.

Half-open. A span that includes its start and excludes its end, [from, to). Every Interval here is half-open, so consecutive intervals tile a timeline without overlapping at the join.

Horizon. The last year a calendar answers exactly, from calendar_through(). na means rule-driven with no horizon. Past a horizon closed_for_holiday() answers Known.UNKNOWN.

In-band. A return value that is a real value of the result range rather than a flag. The reason time_to_close does not return 0 while a session runs: 0 is a real distance.

Instant. A moment on the timeline, as Unix milliseconds. Unambiguous worldwide. Contrast civil time.

ISO week-based year. The year an ISO week belongs to, which disagrees with the calendar year for a few days each January. Pattern letter Y, as against y for the calendar year.

Observance shift. A holiday moved off a weekend to a neighbouring weekday. Different exchanges shift differently, and some do not shift at all.

Offset. A fixed distance from UTC, in hours, carried by a DateTime as a float. Inert: it does not change with the seasons. Contrast zone.

Overlap. The hour that happens twice at a fall-back transition. Resolved by a Resolver.

Period. A calendar-flavoured amount of time: years, months, days. Not convertible to milliseconds without a reference date. java.time's Period.

Proleptic Gregorian. The Gregorian calendar projected backward past its 1582 introduction. Arithmetic, not history: those dates never happened as written, and year 0 exists.

Resolver. The strategy for turning an impossible or ambiguous local time into an instant: COMPATIBLE, EARLIER, LATER, REJECT. Named for Noda Time's ZoneLocalMappingResolver.

Session. A recurring local-time window on selected weekdays, resolved against a calendar. Not a pair of timestamps.

SOQ. Special Opening Quotation. The value Cboe's opening auction in the constituent SPX series prints, which is what VIX settles against, and the reason VIX settlement is a morning instant rather than a close.

Trading day. A day the exchange's calendar says it is open. Weekends and holidays excluded. Not the same as a weekday.

Triple witching. The quarterly expiry in March, June, September and December, when several contract classes expire together.

Unscheduled closure. A market closure no rule predicts: a hurricane, a blackout, a state funeral. Recorded in a dated table, and therefore complete only for the past.

Wither. A method returning a copy with one field changed: with_year, with_month, with_time. Named after the withX convention in java.time. They copy and validate, which is why they are safer than assigning to a field.

Zone. A standard offset plus a daylight-saving rule, so it changes with the seasons. Always a Zone value here, never a float. Contrast offset.

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