OGG is a free, open-source multimedia container format developed by the Xiph.Org Foundation. When referring to audio, "OGG" typically means OGG Vorbis — the Vorbis audio codec stored in an OGG container. Vorbis provides audio quality comparable to MP3 and AAC, without patent restrictions. At equivalent bitrates, Vorbis generally sounds slightly better than MP3.
OGG Vorbis is widely used in gaming (many games use OGG for background music due to the open license), and is the standard audio format for the Wikimedia/Wikipedia ecosystem. It's supported natively in Firefox, Chrome, and Android. However, it's not natively supported in Safari or iOS, requiring a fallback to MP3/AAC for web deployment.
OGG Opus (the Opus codec in an OGG container) is distinct from OGG Vorbis and is significantly more modern. Opus is used by Discord, WhatsApp voice messages, and WebRTC applications because it's excellent at low bitrates (32-64 kbps) for voice content while also supporting high-quality music. For voice calls and voice notes, Opus outperforms both MP3 and AAC at the same bitrate.