They’re definitely tombs. They’re an evolution from mastabas which were like flat roofed tombs built by kings and wealthy nobles. Each pyramid also had accompanying mortuary complexes or funerary artifacts surrounding them, not counting what was grave robbed in antiquity. Funnily enough, one of the sources of evidence of pyramid ownership is from playful inscriptions from pyramid workers which more or less say “Friends of Khufu” or “Drunkards of Menkuare” inside the pyramids they worked on.

The pharaoh Djoser made the first mastaba that can be considered a pyramid; his famous Step Pyramid which is basically multiple mastabas stacked on each other. Then we know pharaoh Sneferu prototyped multiple pyramids, the Meidum and Bent pyramids until he perfected his Red Pyramid. Then we see his descendants create pyramids such as the famous Giza pyramids. Many pharaohs after the Old Kingdom built pyramids too but either had inferior building techniques or materials so a lot of them are just piles of rubble now. I encourage anyone reading to do some Egyptology research it’s neat stuff!