Question on STO_ acronym in ST code

[BTrem.1]

In trying to understand some motor control code in the ST Library I've come across some procedure names with STO_ as a prefix. Simple question what does the acronym STO mean?

[TDK · Accepted solution]

It apparently means "state observer" per:

https://www.st.com/resource/en/user_manual/cd00298474-stm32f-pmsm-singledual-foc-sdk-v43-stmicroelectronics.pdf