Allrun is an executable that is located in most of the OpenFOAM tutorial cases. It is an instruction to the computer on how to run a case. (Basically, it is like a step-by-step IKEA manual on assembling a furniture. Here you are getting the steps that your computer need to carry out to run the simulation.)

Using the Allrun from the simpleFoam motorbike case tutorial (located in $FOAM_TUTORIALS/incompressible/simpleFoam/motorBike) The Allrun script should look like the following (for OpenFOAM v2412):

If the above fails, go through Navigating files in the below may help you in locating your OpenFOAM installation