Processing speed is the pace at which you take in information, make sense of it, and begin to respond. This information can be visual, such as letters and numbers. It can also be auditory, such as spoken language.

Having slow processing speed has nothing to do with how smart kids are—just how fast they can take in and use information. It may take kids who struggle with processing speed a lot longer than other kids to perform tasks, both school-related and in daily life.

https://www.parentcenterhub.org/slow-processing-speed/