When you find yourself on a forum with many American members (such as r/freemasonry on Reddit) you will find many users using such terms as if they are synonyms.
In Anglo Saxon “helan” meant something hidden, or secret, a meaning preserved in “conceal;” “hell,” the hidden place, is from the same word. Helan descended’ from the Latin celare, hide; and on this was built the Latin clandestinus, secret, hidden, furtive. In English clandestine, thus derived, came to mean a bad secret, one that must be indulged in furtively. A secret may be innocent; it is merely something done without the knowledge of others, and nothing is more common; but a clandestine act is one done in such a way as to elude observation. Clandestine Masonry is a bad kind of irregular and unlawful secret society falsely claiming to be Masonic. In the Constitutions a Clandestine Mason is defined as, “One claiming to be a Free and Accepted Mason not having received the degrees in a Lodge recognized as regular by the Grand Lodge of the State of New York.”
Concealed, usually for some secret or illicit purpose. In Freemasonry, illegal, not authorized.
This says this Masonic dictionary with no separate lemmet for “irregular”.
In 1999 the United Grand Lodge made the following statement (my emphasis):
There exist in England and Wales at least two Grand Lodges solely for women. Except that these bodies admit women, they are, so far as can be ascertained, otherwise regular in their practice. There is also one which admits both men and women to membership. They are not recognised by this Grand Lodge and intervisitation may not take place.Source
So a Grand Lodge can be unrecognised, but “regular in their practice”. That doesn’t really make the discussion easier, but it appears to mean that UGLE does not regard the two women-Grand Lodges “irregular”.
The same quote has another interesting sentence: “The Board is also aware that there exist other bodies not directly imitative of pure antient Masonry”. So there is the point of “imitative of pure antient Masonry”.
When an organisation is not “imitative” it is not Freemasonry at all and I guess terms such as “bogus” apply there. Then an organisation can be “regular in their practice” or not even that, for example, because it uses no Grand Architect of the Universe or a Bible.
It all is shaky ground and it is particularly so when you know that within “Continental Freemasonry” different types of lodges can exist within the same Grand Lodge. Lodges with or without a Bible, lodges with or without women.
It takes some investigation to learn how a certain organisations stands to another, so terms would better be used with some care. When you do get a term thrown at you that appears to be off mark, just conclude that your Grand Lodge isn’t recognised by the ‘thrower’ and leave it to that. There can still be friendly relations, ‘half recognition’ as in the case of UGLE, there can be amity, but more often, there may be no official standpoint whatsoever.
To make it even more complicated. When a (new) Grand Lodge contacts other Grand Lodges about recognition, it could be that one agrees and another doesn’t. When you want to know if you can visit lodges of some organisation, best ask you Grand Secretary. (S)he may have to do some investigation, since it is not like every Grand Lodge has a list of all existing (semi-)Masonic organisations listing if they are recognised or not.
A little closing remark about “scam” organisations. There are those who portray themselves as Freemasons, but are only in to get your money. There are also those who actually grand degrees (only on paper or even ‘for real’) for substantial amounts of money. It is hard to draw the line between good, questionable and bad. When in doubt, ask around!