Tracks on a CD are sometimes played as if they are one single track.
No white space between the tracks.
Live albums are an example.
In classical music sometimes consecutive movements are played as one.
In case of CD’s gapless playback is very easy to obtain because there are no tracks.
It works pretty much like an LP, a single groove.
The tracks as we see them om the display is just a table of contents.
In case of computer audio, each individual track of a CD becomes a file.
Gapless playback is a property of the media player to play these files gapless.
Not all media players support this.
Even if the media player supports it, it might not apply to all supported audio formats.
Audio formats with fixed frame length like MP3 will always have some white in the last frame.
Clever programmers can simply concatenate audio files and remove the gap in the process.
Streaming audio players (DLNA) often don’t support gapless playback.
An option to force any media player or streaming audio device to play gapless, is to rip to a single file + cue-sheet.
It has its downsides too. This is discussed here.
Gapless Playback - Hydrogenaudio