Bt in Bt cotton signifies biotechnology.

Explanation

**Step-by-Step Text Solution:**

1. **Understanding Bt Cotton**: Bt cotton is a genetically modified organism (GMO) that has been engineered to express a specific trait. The "Bt" in Bt cotton stands for "Bacillus thuringiensis," which is a bacterium known for its insecticidal properties.

2. **Role of Bacillus thuringiensis**: Bacillus thuringiensis (Bt) produces a protein that is toxic to certain insects. This bacterium is commonly used in agriculture as a natural pesticide.

3. **Toxic Protein Production**: The toxic protein produced by Bt is effective against various pests that threaten cotton crops. The gene responsible for coding this protein is known as the cry gene.

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