flashcard vs trading card

flashcard

noun
  • A card used to aid rote memorization. One side of the card contains data of one kind, or a question, and the other side contains the associated response which one wants to memorize. For example, one side could contain an English word, and the other side the Spanish translation. 

  • A solid-state digital memory storage format, commonly found on computers, digital cameras and cellphones. 

trading card

noun
  • A collectible card, sometimes sticker, usually made out of paperboard or thick paper, which usually contains an image of a certain person, place or thing (fictional or real) and a short description of the picture, along with other text (attacks, statistics, or trivia). There is a wide variation of different types of cards, like sports, cars, natural history, film characters or other information of interest to purchasers. Sometimes is included with tobacco, food or confectionery products. 

How often have the words flashcard and trading card occurred in a corpus of books? (source: Google Ngram Viewer )