Yeah. Acronyms. They make things a little easier to type because things like o11y are a lot faster to write, particularly if you do it a lot, than things like observability. But the flip side of that coin is that if you don't already know what an acronym means, you are at a disadvantage to understanding anything that uses that acronym.
While this little article can't help you to figure out what most of the acronyms of the world mean, it can help with one.
Simply put, o11y is observability.
I hear you. So, let's close that loop, too.
Observability, in general terms, refers to how well the internal states of something can be understood or inferred from the data that thing provides externally.
Observability as it applies to the human body, for instance, might be things like body temperature, skin color, rates of breathing or heart rate, pupil dilation, etc.
Most of the time, though, when people are talking about o11y or observability, they are talking about computer systems. The scale of these systems can span from individual processes to massive infrastructure supporting and internet-scale application deployment. The scale, though, doesn't matter so much.
What matters is the ability to collect data from those systems -- the infrastructure and software equivalents of body temperature, heart rate, and skin tone -- and to use that data to make accurate inferences about the state and the health of the systems internally.
So when someone talks about o11y or observability, they are really just talking about the ability to see inside of another system in order to draw some conclusions about how well the system is working.