It means that your version of
biber is not packaged as a standalone binary, the way
biber is packaged in TeX distributions and for binary downloads from upstream. You presumably instead have a simple
perl programme, which depends on your also having a suitable version of
perl and the various modules required by
biber. Normally, you don't need these to run
biber because the
PAR:Packer module allows a completely self-sufficient version to be distributed. Basically, this unpacks itself into a stand-alone
perl tree when
biber is run. On your system, that won't happen:
biber will be just the
biber bit and the other bits will be elsewhere.
From Biber's manual (p. 49):
Biber is a Perl application which relies heavily on quite a few
modules. It is packaged as a stand-alone binary using the excellent
PAR::Packer module which can pack an entire Perl tree plus
dependencies into one file which acts as a stand-alone binary and is
indistinguishable from such to the end user. You can also simply
download the Perl source and run it as a normal Perl program which
requires you to have a working Perl 5.24+ installation and the ability
to install the pre-requisite modules. You would typically only do this
if you wanted to keep up with all the bleeding- edge git commits
before they had been packaged as a binary. Almost all users will not
want to do this and should use the binaries from their TEX
distribution or downloaded directly from SourceForge in case they need
to use a more recent binary than is included in their TEX
When a binary
biber is run it normally unpacks all the bits it needs into a temporary directory somewhere on your system. This unpacked tree is then reused on later runs, unless the directory is deleted (e.g. rebooting deletes it if it is stored in RAM).
tells you where this is, because it depends on the local configuration. This enables you to remove the directory yourself if necessary (e.g. if the cached files get corrupted).
On my system the command returns
which tells me, among other things, that
biber will take longer to run after a reboot, because this location is in RAM rather than in persistent storage (e.g. a HDD or SSD).