minFree is associated with High Memory state of ESXi 6 or prior to it.
If you are wondering how ESXi is calculating minFree value, here is the math behind it.
Value of minFree is 899 MB for the ESXi host with upto 28 GB RAM.
host with more than 28 GB RAM, minFree is calculated as bellow
minFree = 899 MB (upto 28 GB RAM) + 1% of remaining capacity of RAM in that host.
Like an ESXi host with 100 GB RAM has minFree = 1619 MB
899 MB + 720 MB (1% of 72 GB)