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An intron is a non-coding sequence in a gene.

It is any nucleotide sequence within a gene that is removed by RNA splicing to get the final RNA product of a gene. The term intron refers to both the DNA sequence within a gene, and the corresponding sequence in RNA transcripts.

A spliceosome removes introns from a transcribed pre-mRNA segment (top). This is called 'splicing'. After the introns have been removed (bottom), the mature mRNA sequence is ready for translation.

Sequences of coding DNA which are joined together in the final RNA after RNA splicing are exons. They code for amino acids in the final polypeptide.