\Delta

Δ — a change

Read "delta". Capital delta means "the change in", so ΔW is the amount W changes by.

$\Delta W$ is one object, the update to $W$ , not $\Delta$ multiplied by $W$ . In LoRA, the fine-tuned weights are $W_0 + \Delta W$ , where $\Delta W$ is the learned correction.

Example

W = 5 \to 5.3 \;\Longrightarrow\; \Delta W = 0.3

New value minus old value.

Where the course uses it

2.1 Derivatives: Slopes and the Rules for Finding Them · Module 2, Calculus and Optimizationfirst use
20.3 LoRA and QLoRA · Module 20, Adaptation: Fine-Tuning, LoRA, Distillation

Related terms

LoRA — low-rank adaptationRead "W zero plus alpha over r, B A". Keep the pretrained weights W₀ frozen and learn a small low-rank correction BA to add to them.