Splice junctions are the points where introns (non-coding regions) are removed from the pre-mRNA molecule during splicing, leaving behind the exons (coding regions).

There are two types of splice junctions:

* 5' splice site: This is the junction between the last nucleotide of an exon and the first nucleotide of an intron.

* 3' splice site: This is the junction between the last nucleotide of an intron and the first nucleotide of the next exon.

These splice junctions are important for proper mRNA processing and the production of functional proteins. They are recognized by specific proteins called spliceosome components, which carry out the splicing reaction.

While "junction" can be used more broadly to refer to any point where two parts of an mRNA molecule come together, the most common and specific use is in the context of splice junctions.