What it means
The Transformer is the 'T' in GPT. It introduced the concept of 'Attention'-allowing the model to focus on different parts of a sentence at once (like understanding that 'bank' refers to a river, not money, based on the other words).
Why it matters
Before Transformers, AI read text one word at a time, forgetting the beginning of a long sentence by the end. Transformers allowed models to understand entire documents and contexts, leading to the explosion of capability we see today.