makefile

I am begginer .
I unable to understand this piece of code in Make file for U-boot in
Linux.
Could any one help me

omap5912osk_config :    unconfig
        @$(MKCONFIG) $(@:_config=) arm arm926ejs omap5912osk NULL omap
The makefile is writtten with so many unconfigs.
Please give some link which explains it.


Regards
chiru