This refers to the audio track. 8CH = 7.1 surround sound (Left, Center, Right, Low Frequency Effects, Left Surround, Right Surround, Left Back, Right Back).
: Keeping a complete 007 collection on a single hard drive. Spectre.2015.1080p.10bit.BluRay.8CH.x265.HEVC-PSA
This particular encode is popular among collectors with limited storage space. By using the codec and 10-bit color, the group PSA manages to shrink a 40GB+ Blu-ray disc down to a fraction of its size (usually 2–3GB) while keeping the image sharp enough for most home theater setups. This refers to the audio track