Here's a breakdown:
* Introns: Non-coding regions of pre-mRNA that are removed during RNA splicing. They are essentially "intervening sequences" that don't carry instructions for building proteins.
* Exons: Coding regions of pre-mRNA that are kept and joined together to form the mature mRNA that will be translated into a protein.
The process of removing introns and joining exons is called RNA splicing. This happens in the nucleus before the mRNA leaves to go to the ribosome for protein synthesis.
