Off-peak

[Becky]

not at the most popular and expensive time, when many people are doing or using a particular thing:

[Oralee]

During a period of less use or demand than the maximum (peak), generally overnight.

[latindictionary]

The Off-Peak Return is a type of train ticket used on National Rail services in Great Britain. The ticket was introduced as the Saver Return by British Rail in 1985, being rebranded to its current name on 7 September 2008.