Mature messenger RNA, often abbreviated as mature mRNA is a eukaryotic RNA transcript that has been spliced and processed and is ready for translation in the course of protein synthesis. Unlike the eukaryotic RNA immediately after transcription  known as precursor messenger RNA,  mature mRNA consists exclusively of exons and has all introns removed.
Mature mRNA is also called "mature transcript", "mature RNA" or "mRNA".
The production of a mature mRNA molecule occurs in 3 steps:
# Capping of the 5' end
# Polyadenylation of the 3' end
# RNA Splicing of the introns