Why "Fahrkarte", "Flugkarte" but "BahnCard"?! Anyone knows their Etymologies? Actually "BahnCard" seems to be composed of two nouns ('Bahn' and 'Card') and it expresses this feature with Capital letters and the word "Card" seems to be directly derived from English but the two other examples could also be with capital letters and also the word "Card" instead of "Karte".
"Fahrkarte" and "Flugkarte" (never heard that; usually, it is "Flugticket") are usual general nouns.
"BahnCard" is a product offered by the company Deutsche Bahn, which does not denote your ticket to go by train. Instead, that would be "Zugticket", "Bahnticket", or also just "Fahrkarte".
As with many such products in Germany, they created a compound word from English and German, and even with Camel Case, which is not even allowed for regular german words.
"BahnCard" offers you discounts on every "Zugticket" you purchase: BahnCard 25 = 25 % discount, BahnCard 50 = 50 % discount, and BahnCard 100 = Flatrate.
BahnCard is the product name for a railway travel-card product offered by Deutsche Bahn AG. It is thus considered a name rather than a substantive by German grammar and does not necessarily have to comply with common grammar rules.
The main reason for a Binnenmajuskel (i.e. an upper-case letter in the middle of a substantive) is: trademark legalese. While German law does not allow trademarking "normal", common German words (like "Bahncard", "Regionalexpress" or "Zugticket"), a specific, uncommon way of writing like BahnCard and RegionalExpress can actually be trademarked. This specific trick was (and partially still is, even if it's getting out of fashion somewhat) actually used starting in the 90ies to create product names that were believed to look cool and could be trademarked by quite some companies.
Today it maybe doesn't look that cool anymore, Deutsche Bahn has now changed their main development of trademarks into using a dot, and has created teminology like bahn.comfort and bahn.bonus
In never before heard the term »Flugkarte«. I think you mean »Flugticket« (this is the word that people in Germany, Austria and Switzerland use).
Karte, when used in
Needed to be allowed to (once) ride the bus, train or similar public transports.
Needed to be allowed to (once) enter a concert, exhibition or similar event.
is a ticket.
Normally it is made of paper, normally for one-time-use, to be thrown away after you used it. There are also tickets for a certain number of rides/entries, or tickets that are valid for a day, a week or other periods of time.
But a Karte of course can also be a card, because the English and the German word both derive from the same etymological root (both come from French carte, which came from Italian carta, which came from latin charta, which came from greek χάρτης (chártēs)):
In this meaning you find it in
playing card (for example for games like poker)
In the advertising departments of many German speaking companies people believe, that the German word »Karte« sounds old-fashioned and boring. They think, that the English word »card« sounds more modern and international, with the bonus, that the pronunciation of »card« is almost the same as of »Karte« (the difference is just a weak unpronounced schwa-sound at the end).
So Deutsche Bahn (DB) came up with a product named BahnCard (train card or rail card), and Österreichische Bundesbahnen (ÖBB) made a similar product and named it Vorteilscard (benefit card or advantage card).
The capital C in the middle of the word BahnCard also is a invention of advertising department, in this case of DB. They use capital letters also inside of other words like RegionalExpress (regional express train).
You can not use BahnCard or Vorteilscard to travel by train. Those cards are not tickets. But when you have such a card, you can buy tickets for a lower price (exactly the half price in case of Austrian Vorteilscard; sorry, I don't know details about German BahnCard).
To get such a card you must fill in a form with personal data that will be printed on the card, and you have to pay for it. (In case of Austrian Vorteilscard you pay 99 Euro and the card is valid for one year.)