The word “lizard” is commonly used to refer to any reptile. So, that means an iguana is a lizard, right? Well, if you’re just talking to your friend, sure, but technically, an iguana is not a lizard.
Lizard, or Lacertilia, is a suborder belonging to the order Squamata. Iguanas, on the other hand, are their own genus, belonging to the suborder Iguania. Iguania also belongs to Squamata though, so they are related fairly closely.
Don’t worry too much about calling iguanas “lizards” by accident. I’m sure they won’t mind.