It means you combine things (because it's handy or whatever) in a manner that loses essentially no information. Normally this would just be some kind of modulation. The salient difference being losing information due to technical limitations (SNR, distortion, bandwidth limits) versus designing the system to remove information (lossy).

Contrast: lossy analog compression, e.g. colour TV.

Specifically, PAL-style color subsampling which is more or less YUV 422. They could have fixed it other ways, but they decided to incorporate a quartz glass prism and piezo transducers to realize a 1-scanline physical delay, which they then used to do the analog variant of XORing each line with the one before.