What is the term for the nucleotide sequences that are removed during mrna processing?

The correct answer is: introns

Processing of mRNA is process that occurs only in eukaryotic cells. After the transcription, newly formed mRNA molecule is called and it must be processed into a messenger RNA (mRNA). Processing includes:

•Addition of a 5' cap to the beginning of the RNA

•Polyadenilation- addition of a poly-A tail (tail of A nucleotides) to the end of the RNA

•Splicing- removal of introns and linking the exons

After these steps mRNA is mature and used for the further steps (e.g. translation).

Sometimes some genes are alternatively spliced.