information about rootfs,uImage and u-boot.bin file for armboard

hello,
what is rootfs,uimage and u-boot.bin files?can anyone tell me?

rootfs is the root file system and contains all the directories like etc,
bin, sbin, usr, sys, lib ....

uimage is the cross-compiled kernel image that uboot (uboot.bin) will boot
up.

@devef thanks for reply...is any link on internet for detail information
about this?

http://www.amazon.com/Building-Embedded-Linux-Systems-Yaghmour/dp/059652...

If you search around the internet there are free download links for this
book 2nd edition and maybe even the 3rd edition.

Throwing uimage into Google returns lots of interesting information.