Kim Janey was sworn in as acting mayor of Boston on March 24. She is also one of eight candidates running to be elected as Boston's next mayor in November's municipal election. So, is there a difference between the office she currently holds and the one she seeks? The short answer is yes. As for how they differ? It's complicated.

Janey became the acting mayor because she was serving as president of the Boston City Council at the time of Marty Walsh's departure, as prescribed in the Boston city charter. Section 11B reads in part, "whenever there is a vacancy in the office of mayor from any cause, the president of the city council, while such absence, inability or vacancy continues, shall perform the duties of mayor.”

This applies whether the mayor is out of town for a weekend or he resigns to become U.S. Secretary of Labor with seven months left in his term.

The section goes on to name the position and define its powers. “The person upon whom such duties shall devolve shall be called 'acting mayor' and he shall possess the powers of mayor only in matters not admitting of delay.”

The key phrase that describes the “acting mayor’s” authority, “only in matters not admitting of delay,” is right there in black and white. And as clear as mud.

For starters, what does it even mean?

“Nobody really knows the origins of the phrase,” said attorney and former Boston City Councilor Larry DiCara.

That includes the people who wrote the earliest dictionaries. According to Peter Sokolowski, editor at large for Meriam-Webster in Springfield, Massachusetts, there is not a specific citation for this turn of phrase is any of the bibles of the English language — the Oxford English Dictionary, Samuel Johnson’s 1755 Dictionary or Noah Webster’s 1828 dictionary.

It does appear in some 17th century works of political philosophy, like James Harrington’s "The Commonwealth of Oceana." And it was clearly in the lexicon of some of America’s first lawmakers, like George Washington and Thomas Jefferson, who used it regularly in their correspondence. Here’s Jefferson in an 1805 letter to Dr. John Silby, explaining that he’s been too busy with urgent matters to keep up with his correspondence.

“I have been some time a debtor for your letters of Mar. 20. and Sep. 2. of the last year. a constant pressure of things which will not admit delay prevents my [acknowledging] with punctuality the letters I receive…”

In essence, the phrase “not admitting delay” or “not admitting of delay” is an archaic, and somewhat convoluted way of saying, “can’t wait” or “has to be dealt with right now.”

But once you get your head around the meaning of the phrase, another critical question remains. Who — exactly — determines what matters are admitting of delay, and what ones are not?

In practice, said DiCara, there is some clarity as to what matters are and are not “admitting of delay” at the extreme ends of the spectrum.

If a water main were to break and money needed to be freed up to deal with it, or the deadline to sign and file paperwork for a project already in motion was to arise, those are matters that are clearly “not admitting of delay,” said DiCara.

On the other hand, big, expensive new initiatives proposed out of the blue would not be.

“I'm not sure she can stand in a parking lot and say, ‘By the way, I've decided that we're going to take $10 million dollars and construct a brand new school,’” said DiCara, of Janey. “I don't think that probably is in the cards.”

But what about the city budget Janey proposed in mid-April? Or proposed reforms to the police department that she has said will be a priority for her time in office? Or the countless other decisions that will face the acting mayor in the coming months? Many of them exist in a large gray area somewhere in between.

“The laws that created the city charter over a century ago are really quite instructive as to many matters, although not to this one,” said DiCara.

The fact that this critical phrase is ambiguous was likely intentional, and serves a purpose,” said GBH legal analyst Daniel Medwed, a Northeastern University law professor.

“Phrases like that are very common in the law,” he explained. “Legal scholars often like to call them standards — as opposed to rules. Legislatures will create standards to give judges and executive officials some wiggle room.”

In many instances, more specificity is brought to these “standards” over the course of time, as challenges to the way they are applied are brought to the courts. Medwed cites the common legal standard “proceed with due diligence,” as an example.

Let’s say the law requires a person to “proceed with due diligence” for some action — like filing a claim. A dispute arises. One side believes that taking a year to file that claim was “proceeding with due diligence.” Another party believes it was not. They go to court, and a judge decides who is right, bringing more clarity to what it and what isn’t “due diligence.”

“Over time, the wiggle room becomes narrower and narrower,” he explained.

But in the case “not admitting of delay,” there simply haven’t been many legal challenges, and therefore the standard remains largely undefined.

In 1993, a lawsuit challenging the authority of then-Acting Mayor Tom Menino was brought by the Boston Teachers Union during a teacher’s contract dispute. But that suit was dismissed for lack of standing.

Besides that, you have to look to another time — and another town — for an example.

Back in 1910, J. Edward Barry was serving as acting mayor of Cambridge and, by law at the time, possessed "the powers of mayor only in matters not admitting of delay." He approved of an order to construct an extension of Waverly street in what is today Kendall Square. A citizen, Charles W. Dimick, believed this was a matter that admitted plenty of delay, and challenged in court Barry’s authority to build the road. The Massachusetts Supreme Judicial Court agreed with Dimick and ruled against the acting mayor.

Beyond the very narrow precedent set by that case, the limits on the acting mayor’s authority remain an open question. And with the next mayoral election not until November, we have plenty of time to find out more about what matters Janey believes do not admit delay.