I'm reading lots of statistical anomaly detection articles nowadays. Some of them use frequency of some feature for detecting anomalies on the new trace.
But, something gets my attention in some articles. Authors use "probability of occurrence" usage than just say frequency. Are they doing this for implying some property of that data set or data? Or frequency is another thing and I don't know the difference?
Using the observations in Section III.B, we develop a technique, called Kernel States Modeling (KSM), to automatically detect anomalies using the probability of occurrences of states in traces.
 Murtaza, Syed & Khreich, Wael & Hamou-Lhadj, Abdelwahab & Couture, Mario. (2013). A host-based anomaly detection approach by representing system calls as states of kernel modules. 2013 IEEE 24th International Symposium on Software Reliability Engineering, ISSRE 2013. 431-440. 10.1109/ISSRE.2013.6698896.