https://doi.org/10.1351/goldbook.I03251
The attachment of an entering group to a position in an aromatic compound already carrying a substituent group (other than hydrogen). The entering group may displace that substituent group but may also itself be expelled or migrate to a different position in a subsequent step. The term 'ipso-substitution' is not used, since it is synonymous with substitution. For example: 
where E + is an electrophile and Z is a substituent (other than hydrogen).
See also: cine-substitution, tele-substitution