BERT, or Bidirectional Encoder Representations from Transformers, is a highly adaptable language model capable of being fine-tuned for various language tasks. The model's proficiency in language can be attributed to its training process. A language model is an AI system that predicts the probability of a sequence of words or characters based on statistical patterns it has learned from large amounts of text data. Fine-tuning a model involves adjusting its parameters using additional task-specific data, allowing it to better perform specific tasks while maintaining its general understanding of language.