An interjection is an interruption by another party or parties made during the course of a current statement. It's considered bad social etiquette, but usually relates to a statement objecting or contradicting to the current subject of a statement.
In parliamentary or court reporting, interjections may be required to be included in text to maintain an accurate record.
Examples of interjection
'Current figures....' (interjection) 'Current according to whom?' '... state that unemployment is falling...' (interjection) 'According to your own study of your own figures!'