What does "point mutation" mean?

A point mutation is a change in a single base within a DNA sequence. DNA is made up of molecules called nucleotides, which differ from one to another only in the kind of base they contain. The sequences of the bases are how DNA encodes instructions for the cell.

Point mutations can completely delete the base from the sequence, making the DNA shorter by one base and disrupting sequences further down the strand. They may also replace the base with another base, rendering the instruction they are part of nonsense or telling the cell to stop production of whatever protein for which the instruction was encoded. Point mutations may also be "silent" when the base is replaced by another base of the same kind, preserving the instruction and the integrity of the strand.