explorer is an unlimited travel ticket for all local bus services in Hertfordshire,
and beyond in some cases

It costs £10 for any group of up to 4 people and £7 for 1 person (£3.50 concessions)

It is often cheaper than two adult singles such as when travelling to Heathrow on
Green Line 724 and is useful when your have to use different buses and operators on your journey.

The £4.50 uno day ticket will be cheaper if you are only using uno services.