Define splicing in the context of RNA processing.

Splicing is a crucial step in RNA processing, particularly in the maturation of pre-mRNA into functional mRNA. During this process, non-coding regions called introns are removed from the pre-mRNA transcript, and the coding sequences known as exons are joined together. This splicing event ensures that the resulting mRNA carries only the necessary genetic information required for protein synthesis.

The removal of introns and the ligation of exons are facilitated by a complex known as the spliceosome, which is composed of snRNPs (small nuclear ribonucleoproteins) and various proteins. This precise mechanism is essential for generating a mature mRNA molecule that can then be translated into a protein.

In contrast, the other options refer to different aspects of RNA processing or do not accurately describe splicing. The addition of a poly-A tail is a separate modification that enhances mRNA stability and translation efficiency, while the conversion of pre-mRNA into rRNA represents another form of RNA processing entirely. Therefore, the correct understanding of splicing in the context of RNA processing directly aligns with the definition provided in the correct answer.