Merriam-Webster defines it as thus:

1a

(1)
: a solemn usually formal calling upon God or a god to witness to the truth of what one says or to witness that one sincerely intends to do what one says
(2)
: a solemn attestation of the truth or inviolability of one’s words
The witness took an oath to tell the truth in court.
b
: something (such as a promise) corroborated by an oath
They were required to swear an oath of loyalty.
took the oath of office
2
: an irreverent or careless use of a sacred name
broadly : swear word
He uttered an oath and stormed away.

From Wikipedia:

In the United States, the oath of office for the President is specified in the Constitution (Article II, Section 1):
“I, (name), do solemnly swear (or affirm) that I will faithfully execute the Office of President of the United States, and will to the best of my Ability, preserve, protect and defend the Constitution of the United States.”
The oath may be sworn or affirmed (in which case it is called an affirmation instead of oath). Although not present in the text of the Constitution, it is customary for modern presidents to say “So help me God” after the end of the oath. For officers other than the President, the expression “So help me God” is explicitly prescribed, but the Judiciary Act of 1789 also explains when it can be omitted (specifically for oaths taken by court clerks): “Which words, so help me God, shall be omitted in all cases where an affirmation is admitted instead of an oath.”
The Constitution (Article VI, clause 3) also specifies:
The Senators and Representatives before mentioned, and the members of the several state legislatures, and all executive and judicial officers, both of the United States and of the several states, shall be bound by oath or affirmation, to support this Constitution; but no religious test shall ever be required as a qualification to any office or public trust under the United States.
At the start of each new U.S. Congress, in January of every odd-numbered year, newly elected or re-elected Members of Congress – the entire House of Representatives and one-third of the Senate – must recite an oath:
I, (name), do solemnly swear (or affirm) that I will support and defend the Constitution of the United States against all enemies, foreign and domestic; that I will bear true faith and allegiance to the same; that I take this obligation freely, without any mental reservation or purpose of evasion; and that I will well and faithfully discharge the duties of the office on which I am about to enter. [So help me God.]

This oath is also taken by the Vice President, members of the Cabinet, federal judges and all other civil and military officers and federal employees other than the President.

Blog post by Phoenix:

It is apparent that the section of the oath that seems almost daily violated by politicians is “I will bear true faith and allegiance to the same; that I take this obligation freely, without reservation or purpose of evasion;”

The congress as a whole along with the executive branch has been knowingly presenting legislation contrary to the constitution and then relying on legal challenges to make it to supreme court for final disposition, that folks is still a violation of the oath taken no matter the lawyeristic maneuver of passing legislation as constitutional and waiting for a challenge. If these were your children you would immediately scold for exceeding limits by their hope of getting away with trouble but suffering consequences for only the most egregious just by sheer quantity, its evasive both by congress and by children, both should be accountable.

Below is the most detailed listing of codes covering the subject of congressional oath and penalties for violation,

It is apparent that the section of the oath that seems almost daily violated by politicians is “I will bear true faith and allegiance to the same; that I take this obligation freely, without reservation or purpose of evasion;”

Federal law regulating oath of office by government officials is divided into four parts along with an executive order which further defines the law for purposes of enforcement. 5 U.S.C. 3331, provides the text of the actual oath of office members of Congress are required to take before assuming office. 5 U.S.C. 3333 requires members of Congress sign an affidavit that they have taken the oath of office required by 5 U.S.C. 3331 and have not or will not violate that oath of office during their tenure of office as defined by the third part of the law, 5 U.S.C. 7311 which explicitly makes it a federal criminal offense (and a violation of oath of office) for anyone employed in the United States Government (including members of Congress) to “advocate the overthrow of our constitutional form of government”. The fourth federal law, 18 U.S.C. 1918 provides penalties for violation of oath office described in 5 U.S.C. 7311 which include: (1) removal from office and; (2) confinement or a fine.

The definition of “advocate” is further specified in Executive Order 10450 which for the purposes of enforcement supplements 5 U.S.C. 7311. One provision of Executive Order 10450 specifies it is a violation of 5 U.S.C. 7311 for any person taking the oath of office to advocate “the alteration … of the form of the government of the United States by unconstitutional means.” Our form of government is defined by the Constitution of the United States. It can only be “altered” by constitutional amendment. Thus, according to Executive Order 10450 (and therefore 5 U.S. 7311) any act taken by government officials who have taken the oath of office prescribed by 5 U.S.C. 3331which alters the form of government other by amendment, is a criminal violation of the 5 U.S.C. 7311.

Violating Oath

The subject I am bringing to the table is “why do the American people allow their representatives to break oath of office (a federal crime) and not hold them accountable?

This should be a non-partisan subject simply due to the fact this has been going on for long decades and both parties are guilty according to the law.

The scales could be tipped back somewhat if the public had awareness that the oath has teeth and voiced expectation that it be taken seriously.

I grew up on a rural farm and had an older neighbor and I had just got out of high school in the spring and turned eighteen in the late summer and come the next January, I enlisted in the military service.  The morning I was getting ready to report to boot camp Raymond came over.  I was getting ready to leave for the airport, he came up to me and stuck out his hand.  He said, “You are about to say some pretty big words soon and it will define you as a man.  Good Luck.”

At the time I was stunned, in all the years that I had known Raymond, he had patted me on the back after school football games, other sports, 4H, and at other events but he had never shook my hand till that day.  I had read the oath of service but until you are saying it and what Raymond said actually hit me like a rock.  In his eyes, I had just grown up.

Those words are what you are to live by every day during your service to your country and afterwards.  Why is it that our elected representatives fail to follow their oath of office when they require those in military and civic service to follow theirs.  We have been complacent in letting them tear us down.  We need to stand up and make them follow the same laws and Oaths we do.