Applying knowledge learned on one task or dataset to a different but related task — the principle that makes fine-tuning a pre-trained model far more efficient than training from scratch.
Transfer learning is the practice of taking knowledge a model gained on one task and applying it to a different task. In natural language processing, this almost always means starting from a model that was pre-trained on a large text corpus — BERT, ALBERT, DeBERTa, T5 — and then fine-tuning it on a smaller labelled dataset for a specific job. The pre-trained model has already learned grammar, syntax, and broad world knowledge. Fine-tuning redirects that knowledge toward the target task.
Language understanding is largely transferable. The patterns a model learns to predict masked tokens in general text — syntactic structure, semantic relationships, entity types — are the same patterns useful for classifying query intent or detecting AI-generated writing. The model doesn't start from zero; it starts from an informed representation of language and only needs to learn the task-specific decision boundary on top.
This is why DEJAN can train production-quality classifiers with thousands of labelled examples rather than billions. The heavy lifting — understanding language — was done during pre-training. Fine-tuning is comparatively cheap.
General language understanding transfers well. Domain-specific vocabulary sometimes transfers poorly — a model pre-trained on general web text may not initially handle Dutch legal documents or highly technical SEO jargon as well as a domain-specific pre-trained model would. DEJAN-LM addresses this by pre-training on editorial web content specifically, making it a better starting point for content-quality tasks than a generic BERT.
LoRA and other parameter-efficient fine-tuning methods are extensions of the transfer learning idea: instead of updating all weights during fine-tuning, they train small adapter layers that capture task-specific adjustments while the pre-trained knowledge is preserved in frozen weights.
