Messenger RNA

The ribonucleic acid (RNA) that is directly involved in the transcription of the pattern of bases from the DNA to provide a blueprint for the construction of proteins is called messenger RNA or typically mRNA.

The sequence of bases on a segment of DNA called a gene is copied to a strand of RNA with the assistance of RNA polymerase.

The mRNA produced has regions called introns that are not a part of the pattern for the protein to be produced, so those segments are excised from the mRNA to leave only the segments called exons as preparation for the mRNA's release from the cell nucleus. The pattern for protein synthesis is then read and translated into the language of amino acids for protein construction with the help of transfer RNA or tRNA.

References:
Wiki Messenger RNA