enque/async_req_max is a SAP Parameter attribute which is used to control Max. number of subsequent asynchronous requests 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 .
Some requests to the enqueue server take place asynchronously; this
means the system does not wait for a response from the server. If these
requests are sent in too rapid a sequence, this can lead to an overflow
in the communication buffer, which means requests might be lost. To
prevent this happening, a synchronous request is forced every n
asynchronous request. You specify this number n in this parameter.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.