This is the 214th most frequent Finnish word.
silloin
"At that time" or "then."
In this context, "silloin" specifies a particular time in the past, equivalent to "then" in English.
Minä olin siellä silloin.
I was there then.
Here, "silloin" indicates a specific moment being referred to in indirect speech, implying "at that previous moment."
Hän sanoi, että silloin oli aurinkoista.
He said that it was sunny then.
Here, "silloin" is used to refer to a time that has been defined or specified by the conditional clause, roughly meaning "at that time."