The word "Transit" has two senses in astrology. The first use is more stable; referring to a planet making an aspect to a natal placement, or more generally, the method or predicting the future using such phenomena
https://books.google.com/books?id=guZhAAAAcAAJ&dq=dictionary%20of%20astrology&pg=PA386#v=onepage&q&f=false (Wilson's dictionary of astro. 1819)

(I should also add, this term can also apply to a planet being in a certain pt of the sky in the nativity; so if Gemini is my natal 1st house, & the sun is currently in Gemini, I can say the sun is transiting my natal 1st)

The second term is broader; it refers to a planet being in, a particular area of the sky at a given moment. Take this recent article https://www.astro.com/astrology/opa_article200814_e.htm, which calls the presence of three planets in Capricorn a "transit"

This second, broader sense is also of some antiquity; we find it used in Lilly's Christian Astrology https://books.google.com/books?id=cExRAAAAcAAJ&dq=Christian%20astrology&pg=PA250#v=onepage&q=transit&f=false and https://books.google.com/books?id=cExRAAAAcAAJ&dq=Christian%20astrology&pg=PA440#v=onepage&q=transit&f=false

It should be noted, however, that Lilly also uses the word 'transit' in its restricted, natal sense as well
https://books.google.com/books?id=cExRAAAAcAAJ&dq=Christian%20astrology&pg=PA741#v=onepage&q=transit&f=false

It does not appear that writers of dictionaries, etc. of astrology are aware of the fact that 'transit' is now a polysemous word. The current http://astro.com  article on transits https://www.astro.com/astrowiki/en/Transit only mentions the word's use in its natal context...

... when on that very site we find articles using the word in a mundane context https://www.astro.com/astrology/opa_article200814_e.htm

Indeed, this article here goes so far as to call a three-planet conjunction in Capricorn a 'transit', which is far removed from its traditional sense of 'being in a particular area of the zodiac'

An even wider sense of transit can be found in the almanacs of the Honeycomb Collective. There, they refer to aspects between planets in general as "Mundane transits". They also use transit[ing] as a verb; so ☽☍♇ is referred to as "Transiting moon opposes transiting pluto"

The traditional astrologer would consider this use of the word "transit" redundant- the moon just conjoins pluto; what nativity is there to transit over? But then again it is not a very great leap from "Transiting moon cnj natal pluto"...
(a moving planet meeting a fixed point)

to "Transiting moon conj. transiting pluto" (2 moving planets meeting). It is simply a generalization of the same terminology.

Thus, the word "transit[ing]" signifies the planet is moving in real-time, as opposed to, say, its position in a nativity, which is fixed.

If anything, this shows the almost complete dominance of natal astrology today: general planetary events are viewed through the lens of natal techniques.

You can see this also in the "[least]favourite sign" discourse and this thread https://twitter.com/edwardW2/status/1201812676000833537