Terminal - Is the built in zip command lossy?
No, ZIP files are never compressed in a lossy way, nor would it really even be possible.

Lossy compression algorithms only work for data which can be approximated and still be recognizable to humans. Pictures and audio work for this, but not arbitrary data.

ZIP compression algorithms take arbitrary data, and without knowing what it is, compress it losslessly by finding redundant data, and mapping it out. There would be no way to know what part of the data might be approximated, which is why archive software use lossless compression.