Word or Phrase for the beginning or end of an event or period of time?

Question

I'm looking for a single word to indicate a point in time which is either the beginning or end of an event.

Edit, for a better example: A bell rings at the start a round of boxing. A bell rings at the end of a round of boxing. Assuming the bell rings at no other times, we can say the bell always rings at the BLANK of a round.

Currently, for BLANK, I'm using the phrase "start or end." It feels clunky. I'd like to replace it with a single word, if possible.

Answer 1

Transition can be used to describe a generic change of the software state, including the beginning and end points that mark a state that exists over time.

We use this term transition in engineering to indicate changes from one state (which is ending) to another state (which is beginning).

Transition: passage from one state, stage, subject, or place to another: change;

It can also be used to express changes in abstract phases of operational behavior. For example, the transition from the data collection phase to the data reduction phase clearly marks the point when one phase ends and another phase begins.

Using "transition" would not be in conflict with parallel processes. In the example given above, the data reduction phase can transition from idle to active, even while the data collection phase continues in parallel.

Answer 2

Terminus (plural termini, if you want to be stuffy) is the Latin word for either end of a 1-dimensional extent, and specifically of motion along that dimension. If one uses a Time Is Linear Motion metaphor theme, and considers the timeline of an event, one can talk about the beginning as the terminus a quo 'the terminus from which', and the ending as the terminus ad quem 'the terminus toward which'. These are all established words and phrases in English.

This answer was submitted as a comment by John Lawler.

Answer 3

Any interval has its limits, either in time or space, and there is a right-hand limit or left-hand limit, or max and min, or whatever, but why the "limit" will not suffice?

Answer 4

Epoch — the beginning of a distinctive period in the history of someone or something.

welfare reform was an epoch in the history of U.S. social policy.

It doesn't apply to the end of a period, but the beginning for sure.