A biological particle composed of a nucleic acid core and a protein cover is called a virus.

Here's why:

* Nucleic Acid Core: Viruses contain either DNA or RNA as their genetic material. This core holds the instructions for the virus to replicate and spread.

* Protein Cover (Capsid): This protein shell protects the nucleic acid core and helps the virus attach to and enter host cells.

Viruses are obligate intracellular parasites, meaning they can only reproduce inside the living cells of other organisms.