# 5.2 Terminology

_Peios / Peios technical reference / PGSS / Applications_

> The nouns this chapter is specified in — application, declaration, id, catalogue, program, title, listed, media type pattern, candidate, choice, default.

**Application.** A program as a desktop knows it: something with a
title that can be started from a launcher or opened with. In this
chapter an application is always what a declaration says, and nothing
is an application without one.

**Declaration.** The file that says what an application is, in the form
of §5.3. One file declares one application.

**Id.** The name of an application: the reverse-DNS string the
declaration's file is named for, in the form of an icon identifier
(PGSS Icons §4.3). `dev.peios.gexora` is an id.

**Catalogue.** The directory holding every declaration on the system,
in the form of §5.4. A consumer that wants to know what applications
there are reads it.

**Program.** The file a declaration says to run: an absolute path. The
program is what a consumer executes, and what a consumer matches a
running process against (§5.5).

**Title.** What an application is called wherever a consumer shows it
to a person.

**Listed.** Whether a launcher shows the application among what can be
started. An application that is not listed is still an application: it
can be opened with, and a running one is still named by its
declaration.

**Media type pattern.** Either a media type, `image/png`, or a
top-level type and `*`, `image/*`, which stands for every subtype of
it. A declaration says what an application opens in these.

**Candidate.** An application that says it opens a file's media type,
and so may open the file (§5.6).

**Choice.** A media type pattern and the id of the application chosen
to open it, kept in the registry by a person for themselves or for the
machine as a whole (§5.7).

**Default.** The application a consumer opens a file with when it picks
one: the candidate the choices give the file's type, by the order of
§5.7. A type no usable choice is for has no default.

Terms defined in PGSS Icons (identifier, chain, consumer as one who
draws) are used with the same meaning and are not redefined, and nor are those of the registry (key, value, `REG_SZ`,
`CurrentUser\`), which are the Peios Kernel TRM's, or security
descriptor, which is PCDS's. *Media type* is used as RFC 6838 defines
it. *TOML* is the format at
toml.io, version 1.0.