The suffix "-gnu" does not stand for "glibc".
The triplet defines the calling convention. For example x86_64-linux-gnu means x86_64 / AMD64 CPU architecture, Linux, with standard GNU / GCC calling convention. Other calling conventions are "x86_64-linux-gnux32" for X32 on AMD64 and "arm-linux-gnueabihf" for 32bit ARM with extended ABI and hardware float support.
The triplets are standardized beyond Python. Debian's multiarch page lists and explains a large amount of triplets, https://wiki.debian.org/Multiarch/Tuples