The word hieroglyph comes from two Greek words meaning
In ancient cultures, priests were often the only ones who wrote and their writing was about sacred matters. Hieroglyphs were used to decorate tombs functionally and to keep track of the (divine) pharaoh's possessions. They could be written, as the etymology implies, by being carved into stone or painted or drawn with pen and ink on papyrus. Hieroglyphs are the picture symbols, but the term hieroglyphic is an adjective used to refer to the type of writing. Thus, you could say hieroglyphic writing or simply hieroglyphs, or you could go with what everyone else says -- hieroglyphic. This makes intuitive sense because the other Egyptian writing systems are known as demotic and hieratic, rather than demot and hierat, but that's because they have different etymologies.