free
#------------------------------------------------------------
#total    Total installed memory
#used    Memory currently in use by running processes (used= total – free – buff/cache)
#free    Unused memory (free= total – used – buff/cache)
#shared    Memory shared by multiple processes
#buffers    Memory reserved by the OS to allocate as buffers when process need them
#cached    Recently used files stored in RAM
#buff/cache    Buffers + Cache
#available    Estimation of how much memory is available for starting new applications, without swapping.