An intron is a nucleotide sequence found within the genes and is removed via RNA splicing when a mature RNA molecule is being generated; on the other hand, an exon is a nucleic acid sequence present in a mature messenger RNA molecule. Basically, introns are DNA bases found in between exons while exons can be described as DNA bases which are translated to mRNA.
Both introns and exons are parts of genes. They were independently discovered by Phillip Sharp and Richard Roberts in 1977. Introns are mostly found in multicellular eukaryotes, like humans. They are rarely found in unicellular eukaryotes like yeast.
Since introns are less conserved, their sequence tends to rapidly change over time. Exons are more conserved, meaning their sequence remains unchanged over time or in between the species. An exon is a part of the gene responsible for coding amino acids while introns do not take part in protein coding. Therefore, introns are non-coding areas whereas exons are coding areas.
Introns are found within the gene while exons are always found at the ends of a gene. Exons are the only parts of the gene nucleotide sequence that are expressed in the protein; introns are silent and are not expressed because they interfere with exons.