This article will explain the different counters in the show system memory output.

Following output is seen when you run "show system memory"

root@device> show system memory 

System memory usage distribution:

    Total memory: 100610360 Kbytes (100%)

  Reserved memory: 2533020 Kbytes ( 2%)

    Wired memory: 1204496 Kbytes ( 1%)

   Active memory: 576892 Kbytes ( 0%)

  Inactive memory: 3640396 Kbytes ( 3%)

    Cache memory:    0 Kbytes ( 0%)

    Free memory: 92869316 Kbytes ( 92%)

"show system memory" command will display - Display system-wide memory distribution and usage including the Junos kernel, software processes, and memory disks.

System memory usage distribution -

Amount of memory used by the system, represented in kilobytes and as a percentage of the total memory.

• Total memory—Actual memory available to the system at the time of system initialization.
• Reserved memory—Amount of total memory reserved for the system at the time of system initialization, but not managed by virtual memory sub-system.
• Wired memory—Amount of total memory wired in the system that never paged out.
• Active memory—Amount of total memory actively in use.
• Inactive—Amount of total memory in use, but not referenced recently.
• Used memory—Amount of total memory used.
• Free—Amount of total memory available for allocation.
• Buffer—Amount of memory used as buffers.
• Swap—Amount of virtual memory that is swapped out to a block disk.
• Available—Estimate of how much memory is available for starting new applications without swapping memory. This estimate takes into account that the system needs some page cache to function well. Not all reclaimable slab is reclaimable because certain items are being used.
• Cached—Amount of total memory almost available for allocation.

Memory disk resident memory –

Memory used by the memory disks, but not accounted for in the kernel map. For example, swap-based memory disk.

VM-Kbytes –

Virtual memory used as per all virtual mappings in the kernel or process map and percentage thereof based on maximum addressable virtual memory as per any kernel, system, architecture, or resource limits.

Resident –

Real memory used as per actual resident pages of all mappings in the kernel or process map and percentage thereof based on the total real memory available in the system.

Map-name –

Name of the map.

PID –

Process ID.

Process-name –

Name of the process.

(MX Series routers only) When you display the memory usage for an MX Series Virtual Chassis, the show system memory command does not display information pertaining to the relayd (/usr/sbin/relayd) process.

Refer below technical publication for more details

https://www.juniper.net/documentation/us/en/software/junos/cli-reference/topics/ref/command/show-system-memory.html