Key is

Options

A. A form of herbaria
B. A type of educational institue
C. A taxonomical aid used for identifying various organisms
D. Taxonomic category

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about the definition of "key" in the context of biology and taxonomy.

2. **Identifying the Options**: The options provided are:
- A form of the herbaria
- A type of educational institute
- A taxonomic aid used for identifying various organisms
- A taxonomic category

3. **Analyzing Each Option**:
- **Option 1**: A form of the herbaria - This is incorrect because herbaria are collections of preserved plant specimens, not a form of a key.
- **Option 2**: A type of educational institute - This is also incorrect as a key is not an educational institute.
- **Option 3**: A taxonomic aid used for identifying various organisms - This is correct. A key helps in the identification of organisms based on their characteristics.
- **Option 4**: A taxonomic category - This is incorrect because taxonomic categories refer to the hierarchical classification (like kingdom, phylum, etc.), and a key is not a category.

4. **Conclusion**: The correct answer is that a key is a taxonomic aid used for identifying various organisms.

### Final Answer:
A key is a taxonomic aid used for identifying various organisms.

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