WAP-7 - दिल तुझपे कुर्बान

There is no concrete definition for a junction, but generally in IR (There are quite a few exceptions) the idea is that the station or cabin that controls the signals and switches at the point of diversion is labelled as a junction.
For example, see the attached screenshot of the track layout in Chennai. This is the layout at Chennai outskirts. On the left (Vyasarpadi - VJM) is the mainline towards Coimbatore, on the top (Korukkupet-KOK) is the mainline towards BZA/HWH/NDLS, on the right (Washermanpet - WMT) is the mainline towards Chennai Egmore/TPJ/MDU. On the bottom (Basin bridge-BBQ)) is a short section that terminates at Chennai Central (MAS).
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As you can see, all possible track connections have been made at this place, and all four stations (VJM, KOK, WMT and BBQ) have 4 FEDL lines branching out of them in different directions. But only Basin Bridge is termed a 'junction' while the others are not. This is because the central signalling system at BBQ controls all the signalling and track switches at these points. In fact, most of the suburban signalling in Chennai is controlled centrally from BBQ. So, at all the other stations, even though there are tracks diverting in different directions, note that the station itself does not have any control on the direction of movement of the trains.
Passengers can obviously get down at say, Washermanpet and switch to a train going in a different direction (essentially WMT is a 'junction' point for passengers), but as far as the station itself is concerned, the staff at WMT do not have any control on which direction the train takes after BBQ. So, WMT is technically not a junction as far as the operation staff are concerned.
Not just here, but in many suburban sections, we see that though there are a lot of lines branching out at various stations, there will pretty much be only 2 or 3 stations that are termed as junctions. While there are a few exceptions to this, in general, stations which do not control the flow of traffic through them are not termed as junctions.