These are the terms used in configuration files, logs and players. Check where each term appears: a counter in a source client may measure something different from a similarly named Icecast field. The linked guides explain the relevant steps.
Source client
The application that encodes or reads media and sends it to Icecast. It is a separate process from the distribution server.
Mountpoint
The exact URL path associated with a stream, such as /live.ogg. It does not have to be a disk file.
Listener
A client receiving a stream. Current listener connections are different from the cumulative number of connection attempts.
Client
A broader connection category that can include listeners, web requests and administration access. Do not equate it with audience size.
Relay
A receiving server that pulls a stream from an upstream and redistributes it. A relay does not transcode the stream.
Upstream
The origin feed requested by a relay. Its remote path can differ from the mount offered by the receiving server.
Fallback
A configured alternative destination for listeners when their requested stream is unavailable or meets a configured overflow condition.
Intro
Media sent before the main stream to a new listener. Its format must be compatible; it is not the same as a fallback.
Container
The structure carrying media streams and metadata. Ogg and WebM are containers; Vorbis and Opus are codecs.
Codec
The media encoding method. Changing a filename or MIME label does not convert one codec into another.
Content-Type
The HTTP media-type declaration describing the delivered representation. It must agree with the actual media bytes.
M3U playlist
A text playlist containing a stream reference. It is not the stream data and is not limited to MP3.
ICY metadata
Metadata blocks carried at agreed byte intervals in applicable legacy streams. They are different from an Ogg container’s metadata.
HTTP PUT
A source upload method supported by current Icecast. The source application must still send a suitable continuous media stream.
SOURCE method
The older Icecast source-connection method. It should not be confused with a file named source or every encoder’s output mode.
Queue
Server-side buffered stream data that accommodates temporary listener lag. Its byte limit is not a guaranteed latency target.
Burst
Initial buffered bytes offered to a newly connected listener, helping fill the player buffer. Keep the burst smaller than the configured queue.
TLS
Transport encryption and server authentication when correctly configured. HTTP Basic authentication alone does not provide encryption.
Authentication role
In 2.5, a combination of request selection, an authenticator and access policy. Matching and permission remain separate concepts.
CORS
Browser-origin access rules conveyed through HTTP headers. CORS does not authenticate a listener or make a public URL private.
XSLT
A transformation language used to render Icecast XML statistics into HTML or other formats. Public output should be deliberately limited.
YP directory
A public stream catalogue. Publication requires valid stream information and a reachable advertised URL; it is separate from streaming itself.
IceS and libshout
IceS is a separate source application; libshout is a library for source software. Neither version number identifies the Icecast server release.