BadMEM is successor of BadRAM patch, made to work on new Linux kernels.
BadMEM allows Linux kernel to use partially broken memory. The idea is that the user should scan the memory with program like memtest86 and load the Linux kernel with the BadMEM parameters the program gives. Thus, the kernel knows which part of the memory is fried and will not use that.
Some people amuse non-Linux-users by buying tons of broken memory chips cheap, stuffing them to the computer, using this patch and typing "free"... (Health advisory: fully working RAM is cheap these days, too. =)