Definition:
Hieroglyphs are the ancient Egyptian signs used for writing. Many of the signs used are recognisable pictures of people, body parts, animals, birds, plants, etc., although there quite a few hieroglyphs which require explanation - the significance that the object had for ancient Egyptians is no longer true today and the picture can seem obscure.
There are around 500 commonly used hieroglyphs, but during the Ptolemaic era the number had risen to several thousand. Hieroglyphs are categorised according to a table published by Sir Alan Gardiner, a British Egyptologist, in 1927.
Note that hieroglyph is a noun and hieroglyphic is an adjective. We write: 'this sign is a hieroglyph' or 'this is a hieroglyphic sign'.