From Eterna Wiki

An intron is a section of the sequence in an mRNA which is not meant to be part of the end product and will usually be cut out before the mRNA can be translated into a protein. Sometimes the gene gets cut alternatively (in a process called alternative splicing). A gene can have different functions, depending on which sections get cut out. It is an efficient way of having the same DNA sequence coding for different versions of the genes, so some versions of it can be used in early development, and other versions can be used in adults.

Teaching about Introns

RNA Processing in a Eukaryotic Cell: Splicing of Introns & Exons