The definitions of a railway junction are many. In general, we say that a junction is where three or more lines meet.
A more detailed definition is given by my friend DSP Anirudh:
“In the company-era railways, the stations at the boundary between the railway networks of 2 different companies, were also called Junctions.
This reflects the more generic meaning of Junction, which refers to a point where two or more things are joined. In railway parlance, this meant that even passing stations (with no branch lines and no break of gauge) could also be termed as Junctions as long as there was something different about the railway lines on either side of the station.”
However, there are also “pseudo-junctions” where one line ends and another one starts, where they are of different gauges. So passengers and freight would have to be transferred at this point.
We look at the pseudo-junctions which existed since 1950. If we go further back many instances can be found in the years while the IR system was expanding.
Kalka and Mettupalaiyam are the most obvious ones, with BG/MG and BG/NG. These will continue indefinitely as long as the mountain railways are running.
Not Neral, NJP, Siliguri and Pathankot as they are junctions in the normal sense as three or more lines are meeting.
One which existed until the 1990s was Parli Vaijnath, where a BG line from Vikarabad met a MG line from Parbhani. Now the MG line is converted.
One which still exists (from 2005) is Udaipur City, where the MG line from Ajmer side was converted to BG and the MG line to Ahmedabad side remained. This was a relatively new line which was opened in the mid-60s. However, the line from Ahmedabad via Himatnagar is partly converted and may be fully BG by 2021. So this, like Parli Vaijnath, will become a wayside station on BG.
Others which will exist for a year or so are Bahraich and Mhow (Dr Ambedkar Nagar).
You may be thinking of Miraj, but that was a junction in the normal sense with branches to Kolhapur and Kurduwadi.
Shantipur on ER had this status until a few years ago, when the BG line from Ranaghat met the NG line to Krishnanagar and Nabadwip. Now the NG line is being converted and there is no longer a BG-NG connection at Shantipur.
A short-term BG-NG junction existed at Balgona for a year or so in the course of the NG to BG conversion of the Barddhaman-Katwa section. Now the conversion is completed.
You may think that New Bongaigaon was where BG ended and MG started between the mid-60s and early 80s. This is incorrect as the BG branch from NBQ to Jogighopa was also opened in the mid-60s, but did not have passenger service for a long time. Local trains were there in the early 70s.
Viramgam was where BG ended until the 1970s, but more than one MG line ended there.
Jaynagar on the Bihar-Nepal border would not qualify since the IR station (MG, then BG) was at a different location from the NG line of the Nepal Railways. I don’t know if there is any change now. The new BG line from Jaynagar to Janakpur and beyond does not seem to have opened yet.
If you go back to the time of independence, there was a BG-NG connection at the OLD Siliguri, where the BG line from Sealdah via Haldibari ended and the NG line started. The NEW Siliguri Jn was built to the north of this, near the old station of Siliguri Road.
At this time, Kishanganj was the end of a MG branch from Katihar and Barsoi and the NG line to old Siliguri started from there.
If you count cases where only passengers had to move from one gauge to another, we can include Madras Beach in the past. For a while, the BG Ganga Kaveri Express used to end there and the corresponding MG train to Rameswaram would start from there.
Also Coimbatore, as it was the end of MG lines from the Pollachi side. The MG lines continued to a point near Coimbatore North.
Many other cases can be found from the earlier days. The weirdest case in undivided India was probably in the Bolan Pass connecting Quetta to the Indus Valley, where there was a small MG section in the middle of the pass between two BG lines. This MG section between Hirok and Kolpur did not last long. During that time (in the late 19th century) passengers and goods were transhipped at both these stations.
This is incomplete, but it is probably not feasible to include all such cases which occurred in the course of lengthy gauge conversion projects.