can any one define all these fields

like what is active? inactive? etc

i can try (some answers are different for different version kernels i thik) and my knowledge is limited

MemShared: always 0 ?? just a leftover old thing
Buffers: buffer cache == i think this is delayed buffered disk writes in the block device layer-- mapped pages in page cache write to this buffer cache when a page write is requested rather than to actual physical i/o
and then the physical i/o request goes to a scheduler cue
Cached: memory page cache == i think this is very related to the address space concept and data i/o to the file system again in the block device layer. writes and reads go through the memory page cache like a memory map with buffer cache as an intermediary on writes ? it's like a memorymap if the harddrive.
SwapCached: swaped out then swaped back in so it exists both places
Active: this is the kernel keeping track of what's been used recently or presently being used as opposed to
Inactive: which is junk that can be tossed or swapped out if need be
HighTotal: i'm not sure how much detail to go into here but generally the linux kernel maps to 1 gb physical ram. if you have more than 1 gb of physical ram then the kernel needs aditional non-permanent map structures to map more physical ram to it's virtual address space, this is called zone highmem