What does the timestamp 90K mean?

Look at Haikang h9 camera opdevsdk_pos.h, There's a 90K Time stamp , I don't know what it means ...

You can refer to this article ：
TS In the timestamp of 90K

When making changes , There is one 90K, This is TS Standard requirements .
If the video is 30 Frames per second , Then one frame of image is transmitted at a time , Then the timestamp increases 90000/30 = 3000、
If the video is 25 Frames per second , Then one frame of image is transmitted at a time , Then the timestamp increases 90000/25 = 3600、
PTS,DTS It is the audio and video synchronization timestamp , A timestamp is actually a sample of particles ( Simple understanding is data ), Take video as an example , Video synchronization clock 90K hz（27M/300）, If the frame rate is 25fps Words , One frame data sampling time 40ms（=1000ms/25）, So the timestamp is 90K x 40ms = 3600（ Estimate ）.
The standard specifies in the original audio and video streams ,
PTS The interval between cannot exceed 0.7s,
Appear in the TS Baotou PCR The interval cannot exceed 0.1s.