binfmt_misc (Miscellaneous Binary Format) is a capability of the Linux kernel which allows arbitrary executable file formats to be recognized and passed to certain user space applications, such as emulators and virtual machines.
[1] It is one of a number of binary format handlers in the kernel that are involved in preparing a user-space program to run.
[2] The executable formats are registered through the special purpose file system binfmt_misc file-system interface (usually mounted under part of /proc).
This is either done directly by sending special sequences to the register procfs file or using a wrapper like Debian-based distributions binfmt-support package[3] or systemd's systemd-binfmt.service.
[4][5] The register file contains lines which define executable types to be handled.