.properties, a file extension mainly used in Java

HOCON, a superset of .properties and JSON

INI file, a common configuration file format

JSON, with support for complex data types and data structures

Run commands, which explains the historical origin of the "rc" suffix

TOML, a formally-specified configuration file format

YAML, with support for complex data types and structures

image configuration file

define configuration file

wikipedia configuration file

weblio configuration file

kotobank configuration file

jisho configuration file