This question comes up on Reddit all the time: if Transformers are made of metal, are they robots? The franchise's answer is clear — they are alive, just not organic.
What makes them alive
Every Transformer has a spark — the source of consciousness and personality. They are born (from the Well of All Sparks or the AllSpark), grow, feel, make mistakes and die. Their bodies are mechanical, but they behave like any living being.
How they differ from robots
A classic robot runs a program. Transformers have free will: they choose factions, change their views, betray and forgive. In many stories they even take offence at being called 'robots'.
Biology, but metal
Many versions describe organ analogues: a brain module, fuel lines and, in some comics, even Energon 'blood'. That's why fans sometimes call them a mechanical life form rather than machines.
Conclusion
Transformers are an alien race that's simply made of different material. That's what makes their stories interesting: not a war of machines, but a war of peoples.
