The Motorolla 68060 is the biggest member of the 68000 processor family, a.k.a. 68k. An accelerator is an expansion card for the Amiga which contains a faster processor than that on the motherboard and usually some more features like RAM and SCSI.
Accelerators for the Amiga were made all the time and I think in 1996 even the CyberStormPPC / BlizzardPPC, i.e. the greatest accelerators ever, were already available or at least advertised.
So if your Amiga contains an accelerator card with a 68060 processor, then the Install disk will not boot because the processor support software it contains (68040.library) does not run on a 68060.