Tram = small train, usually carrying passengers on short urban journeys, with some or all of its route on tracks running along streets. Trams operate in the Croydon area, in the Southern suburbs of London. They are not used in any other parts of London.
Tube = Name often used to mean the London Underground railway system (although strictly only the Central, Bakerloo, Jubilee, Northern, and Piccadilly lines are of tube-type construction).
Travelcard - a ticket giving unlimited travel on all local public transport in specified zones of London. This is valid on the Underground, on National Rail trains, on Docklands Light Railway trains, on trams and on buses. There are eight zones from zone 1 in the centre to Zone 8 on the outermost suburbs. Travelcards can be bought for any combination of these (e.g. zone 1 only, zones 1-4, zones 3-6, etc). They can be bought for one day, for a week, a month or a year.
Bus and Tram Pass = ticket giving unlimited travel on buses and trams in London (but not valid on trains). These cover the whole of London (not restricted by zones) and can be bought for one day, for a week, a month or a year.