The clock speed of the CPU, which is generally significantly higher than the speed of the buses that connect to it. See system bus.
"core frequency." YourDictionary, n.d. Web. 24 May 2018. <http://www.yourdictionary.com/core-frequency>.
core frequency. (n.d.). Retrieved May 24th, 2018, from http://www.yourdictionary.com/core-frequency