-C is for combined -A and -B
Example:
$ grep -C3 systemd /etc/passwd
Output:
gnats:x:41:41:Gnats Bug-Reporting System (admin):/var/lib/gnats:/usr/sbin/nologin
nobody:x:65534:65534:nobody:/nonexistent:/usr/sbin/nologin
_apt:x:100:65534::/nonexistent:/usr/sbin/nologin
systemd-timesync:x:101:102:systemd Time Synchronization,,,:/run/systemd:/usr/sbin/nologin
systemd-network:x:102:103:systemd Network Management,,,:/run/systemd:/usr/sbin/nologin
systemd-resolve:x:103:104:systemd Resolver,,,:/run/systemd:/usr/sbin/nologin
messagebus:x:104:110::/nonexistent:/usr/sbin/nologin
dnsmasq:x:105:65534:dnsmasq,,,:/var/lib/misc:/usr/sbin/nologin
usbmux:x:106:46:usbmux daemon,,,:/var/lib/usbmux:/usr/sbin/nologin
--
colord:x:112:119:colord colour management daemon,,,:/var/lib/colord:/usr/sbin/nologin
lightdm:x:113:120:Light Display Manager:/var/lib/lightdm:/bin/false
dmitritelinov:x:1000:1000:Dmitri Telinov,,,:/home/dmitritelinov:/bin/bash
systemd-coredump:x:999:999:systemd Core Dumper:/:/usr/sbin/nologin
nvpd:x:114:121:NVIDIA Persistence Daemon,,,:/var/run/nvpd/:/usr/sbin/nologin
libvirt-qemu:x:64055:106:Libvirt Qemu,,,:/var/lib/libvirt:/usr/sbin/nologin
_rpc:x:115:65534::/run/rpcbind:/usr/sbin/nologin