Splicing is a alteration of the nascent pre-messenger RNA (pre-mRNA) transcript in which introns are removed and exons are joined together (ligation).

For nuclear-encoded genes, splicing takes place within the nucleus after or concurrently with transcription (genetics).

Splicing for the characteristic eukaryotic messenger RNA (mRNA) is needed before it can be used to produce the correct protein through translation (biology)

Several methods of RNA splicing occur in nature; the type of splicing depends on the structure of the spliced intron and the catalysts required for splicing to occur.

Spliceosomal
Self-splicing
Self-splicing occurs for uncommon introns that form a ribozyme, performing the functions of the spliceosome by RNA alone. There are 3 kinds of self-splicing introns, Group I, Group II and Group III.

tRNA splicing
tRNA (also tRNA-like) splicing is another uncommon form of splicing that usually occurs in tRNA. The splicing reaction contains a different biochemistry than the spliceosomal and self-splicing pathways.
Splicing errors

It has been suggested that one third of all disease-causing mutations impact on aplicing. Common errors include:

Mutation of a splice site resulting in loss of function of that site. Results in contact of a premature stop codon, loss of an exon, or inclusion of an intron.
Mutation of a splice site reducing specificity. May result in variation in the splice location, causing insertion or deletion of amino acids, or most likely, a disruption of the reading frame

Displacement of a splice site, leading to inclusion or exclusion of more RNA than expected, resulting in longer or shorter exons.