Illustrated Glossary of Organic Chemistry

Ipso substitution: Substitution of an aromatic ring substituent (i.e., an attachment other than hydrogen). The mechanism is usually nucleophilic aromatic substitution, but ipso substitution by an electrophilic aromatic substitution mechanism is also possible.

Ipso substitution of fluoride via nucleophilic aromatic substitution mechanism.

Ipso substitution of a TMS group via electrophilic aromatic substitution mechanism.