Lossless audio is a digital file format that compresses sound without throwing away any information. When you play it back, the audio is mathematically identical to the original recording, down to the last data bit.
The key difference from lossy formats (like MP3 or AAC) is that lossless algorithms use reversible compression. They find and remove redundancy in the data, but they can rebuild the original sound perfectly. Common lossless formats include FLAC, Apple Lossless Audio Codec (ALAC), WAV, and WavPack.
A real-world example: if you rip a CD to FLAC, you get identical audio quality to the disc itself, but the file is about half the size. Rip the same CD to MP3, and the file is smaller still, but the algorithm has discarded information you cannot recover.
Lossless matters most to serious music listeners with good equipment. On average headphones or earbuds, the difference between lossless and high-quality lossy (like Spotify's Premium stream or a 320 kbps MP3) is hard to hear. However, lossless is the only choice if you want to preserve studio quality or edit audio later.
When buying music or choosing a streaming service, check whether they support lossless download or streaming. Services like Apple Music and TIDAL offer lossless tiers. Desktop software and high-end portable players are more likely to support FLAC than smartphones. If storage space is tight, lossless files demand more room than lossy alternatives.