MemFree: Free RAM portioan
Buffers: Temporary storage for raw disk blocks
Cached: In-memory cache for files read
SwapCached: Memory that once was swapped out, is swapped back in but still also is in the swapfile (if memory is needed it doesn't need to be swapped out AGAIN because it is already in the swapfile. This saves I/O)
Active: Memory that has been used more recently and usually not reclaimed unless absolutely necessary.
Inactive: Memory which has been less recently used. It is more eligible to be reclaimed for other purposes
SwapFree: Memory which has been evicted from RAM, and is temporarily on the disk
Dirty: Memory which is waiting to get written back to the disk
Writeback: Memory which is actively being written back to the disk
AnonPages: Non-file backed pages mapped into userspace page tables
Mapped: files which have been mmaped, such as libraries
Slab: in-kernel data structures cache
SReclaimable: Part of Slab, that might be reclaimed, such as caches
SUnreclaim: Part of Slab, that cannot be reclaimed on memory pressure
PageTables: Amount of memory dedicated to the lowest level of page tables.
NFS_Unstable: NFS pages sent to the server, but not yet committed to stable storage
Bounce: Memory used for block device "bounce buffers"
WritebackTmp: Memory used by FUSE for temporary writeback buffers
VmallocTotal: total size of vmalloc memory area
VmallocUsed: amount of vmalloc area which is used
VmallocChunk: largest contiguous block of vmalloc area which is free