In this article (sorry its german) I read about camera sensors. They show values like 1,4 µm Pixel, or 1,55 Pixel. What does this mean, and how is it related to sensor size? If I got it right, a bigger sensor is better. For example this sensor has 1/2.55" in size, which is smaller than for example the IMX260 with size 1/2.5". But what about this measure of pixels, and what does it says about image quality?
It is the size of one pixel. 1 µm (micrometer) is a 1/1000.000 part of meter (there are 1000.000 micrometer in one meter).
There is no (direct) relation to sensor size. But knowing sensor size and pixel size you can (roughly) calculate resolution.
The smaller pixels are, the more details are (theoretically) possible on photos. Unfortunately, smaller pixels lead to more noise on photos.
Pixel size is just the area of each pixel in the sensor. It has no direct relation to sensor size, but the more pixels you pack in a sensor size, the smaller they have to be to fit into the sensor.
In general terms there is a correlation between sensor size and some aspects of image quality like noise and dynamic range. There are exceptions, but in general the bigger the sensor (all other factors equal) the less noise the image has.
One very common misconception is that pixel size has direct effect on image noise. As Tony Nortrhup explains on this video https://www.youtube.com/watch?v=_KYvp8PrCFc&t=1s there is no correlation between pixel size and noise because if the sensor is of the same size, smaller pixels are compensated by a greater number of them.