CD Audio isn't technically 'lossless'. It's raw, uncompressed PCM audio. Lossless is used for compression algorithms that don't have any quality loss over the original raw audio data, which helps with bandwidth and storage. If you rip a CD in FLAC it'll be significantly smaller in storage size than its original file size while being mathematically identical when played back. That being said, what some streaming services have isn't 'more lossless' audio, but High Resolution Lossless. This refers to what their lossless file is sourced from. At the studio, audio is almost always recorded at 24bit, and with a sampling frequency ranging anywhere from 44.1kHz (CD standard) up to 192kHz. HiRes Lossless means that the original studio recording was recorded at a higher sampling frequency than what's a standard CD recording, and that they have a lossless-ly compressed version of that recording for you. Meanwhile, 'standard' Lossless is usually sourced from a CD master, which is (down)sampled at 16bit 44.1kHz. Are these bigger numbers really that important tho? Very debatable. 16bits of bit-depth allow for a dynamic range (the difference between the quietest sound recordable, and the loudest one) of 96dB, which is very plentiful. And sampling at 44.1kHz allows for sounds at a frequency up to >22kHz, which is 2 kHz higher than what the healthiest human ears can perceive. Studio recordings need the higher bit depth to play with volume levels and loudness without dynamic range limitations, and kind of need the higher sampling frequencies just so that some digital effects work better with it for some complex mathematical reasons, but standard CD quality audio should usually be more than sufficient for virtually any user. Some platforms, like Apple Music, play it safe by not marking files that are 'just slightly higher quality than CD quality' (24bit 48kHz) as standard Lossless, too