It means companies with US government contracts writing Go code can use the standard library crypto package in native Go instead if having to enable CGO and using a crypto library written in C. CGO is kind of a pain in the ass to develop with compared to fully native Go code, especially when cross-compiling (and cross compilation is very common now that ARM is common on both laptops and servers).

This also now makes Go a very convenient language to write US Gov software in.

If you have never heard of FIPS before ignore this entirely and continue to live in happiness.