The "14" likely refers to the year of release (2014). In the context of networking, this was a stable era, post the initial virtualization boom but pre the widespread adoption of "cloud-native" architectures. It represents a mature phase of the Junos operating system. The "R4" denotes the fourth major release of that train, and the "8" signifies the eighth set of patches and fixes.
: Navigate to the Juniper Networks Support site. --- Jinstall-vmx-14.1r4.8-domestic.img Download