ipc/evt_os_key_bottom is a SAP Parameter attribute which is used to control Lowest Key Number of OS Event Keys information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
An SAP instance uses operating system events from a defined range. This
range starts with a number, such as 3000000 or 4000000. This number is
defined with this parameter. An event has the format X<(><<)>NN><(>
<<)>yyyy>, where NN is the instance number.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.