Definition from Wiktionary, the free dictionary
Silloin, kun olin lapsi, televisiota ei vielä oltu keksitty.
- When I was a child, television had not been invented yet.
The term silloin kun may be used in lieu of kun (“when”) if the speaker wants to stress that he/she is referring to the temporal aspect of the conjunction kun. The word silloin does not convey additional meaning and may be omitted.