Effective date
The day a rule starts to bind, which is rarely the day it was published and rarely the day compliance is measured.
A single rule carries several dates and they are routinely conflated. The publication date is when the document appeared in the Federal Register. The effective date is when the rule becomes operative law. A compliance date, where one exists, is when a regulated party must actually be in conformity, and it can fall months or years after the rule takes effect.
The gaps are deliberate. Agencies use them to give affected parties time to build systems, and they use staggered compliance dates to phase an obligation in by company size or product category. A rule that is effective in thirty days but requires compliance in three years is a common shape, and describing it as taking effect in three years is simply wrong.
Effective dates are also where a change of administration shows up first. Incoming administrations routinely delay the effective dates of rules published but not yet operative, which is itself an action reviewable under the Administrative Procedure Act. Whenever an article here says a rule takes effect, it means the specific date in the document, not an approximation.
What the federal government did, once a day.
One email each weekday: the rules, filings, votes and Fed decisions that actually changed something, each one linked to the document it came from.