You need a program like WinRAR or 7-Zip to extract it.
If you downloaded a file named (or something similar), it is a compressed archive containing other files. 53860 rar
Because "53860" and ".rar" can refer to very different things depending on your specific situation, the term most likely points to one of the following contexts: You need a program like WinRAR or 7-Zip to extract it
Part number 89661-53860 belongs to a Denso Engine Control Unit (ECU) mapped for a Lexus IS 250 (2.5L engine). 53860 rar