Configuration settings: customize applications towards the users' needs. It fulfills following properties:
- It is provided by the execution environment.
- It can be changed by the maintainer, user, or system administrator of the software.
- It consists of a key name, a configuration value, and potentially metadata.
A configuration file: is a file containing configuration settings.
Configuration storage: makes configuration settings persistent. The application will read the configuration at every start from the configuration storage, but it is only stored if a user changes settings.
Key databases: are used for configuration storages because of these constraints. They can do fast key lookups and the keys can be structured hierarchically by defining separators in the key names.
Global key database: provides global access to all configuration storages of all applications in a system. Abbreviated as KDB.
LibElektra: is a set of libraries to access configuration parameters in a global, hierarchical key database.
SpecElektra: is a specification language that allows us to describe the content of the global key database.
Elektra: is a framework consisting of LibElektra, SpecElektra, and a collection of tools.
To elektrify an application: to change the application so that it uses LibElektra afterwards.
Elektra Initiative: is a community that develops LibElektra, expands SpecElektra, improves Elektra's tooling and helps to elektrify applications.
Option, more specifically Command-line option: is a special argument passed on the command-line. Short options are single characters prefixed with '-'; Long options are arbitrarily long and start with '–'.
Module: The parts Elektra is composed of, i.e. either lib, plugin, backend, tool.
Class: A group of functions that logically belong together, working on the same type of objects. A library may implement several classes. E.g., KDB, Key and KeySet are the most important classes.

Technical Concepts

Backends: A collection of plugins to be mounted. A backend typically is responsible to read and write a configuration file.
Bootstrapping: To read the mounting configuration and mount during kdbOpen().
Cascading: To consider multiple places to look for a key.
Contracts: Contracts state the purpose, functionality and requirements of plugins.
Mounting: To persistently and permanently include a backend in the global key database. The mountpoint is the key where the backend is mounted to. All keys of the backend are below that key.
Key name: All keys in the KDB have a name. This name is the keys unique identifier and follows a particular structure. For more information take look at the keyname documentation.
Key name part: Key names consist of a series parts (and a namespace).
Key base name: The last part of a key name.
Key dir name: The key name obtained by omitting both namespace and base name from a key name.
Namespaces: Allow us to have multiple keys for the same purpose and otherwise the same key name.
Plugins: The unit of implementation for a feature.
Metadata: Allows us to describe configuration settings.
persistent name/value/metadata: How it is actually stored, i.e. the state returned by and passed to the storage plugins.
transient name/value/metadata: How it is at runtime, i.e. what is returned by kdbGet and passed to kdbSet.
intermediate name/value/metadata: Any state inbetween the two.

Details

Sync Flag: Marks keys that were changed and need to be written out to disc.
Null Value: The absence of a value, i.e. keyValue (key) == NULL.
pop: Used in ksPop() and KDB_O_POP means to remove a key from a keyset.
delete: or abbr. del, used in keyDel(), ksDel() and KDB_O_DEL means to free a key or keyset. The memory can be used for something else afterwards.
remove: Means that the key-value information in the physical database will be removed permanently. Also used to describe removing a particular key from a keyset.