Nucleic acids are biopolymers that carry genetic information. They are made up of long chains of repeating monomers called nucleotides. Each nucleotide consists of:

* A nitrogenous base: Adenine (A), guanine (G), cytosine (C), thymine (T) (in DNA), or uracil (U) (in RNA)

* A five-carbon sugar: Deoxyribose (in DNA) or ribose (in RNA)

* A phosphate group

The sequence of nucleotides in a nucleic acid molecule carries the genetic code, which determines the sequence of amino acids in proteins.

Here's a simplified definition:

Nucleic acids are the molecules that store and transmit genetic information in living organisms.