For those not familiar with the term, there are different interpretations of what is meant by type collecting (like Leon mentioned), and the word should be given its ordinary meaning. I start with the question of “what type of card is that?” and expand from there. If I have a 1916 Sporting News Dave Bancroft and you have what appears to be the same card but with a blank back, some would say we have the same type– a card of a particular size denoting the same picture/subject and caption. Others would say that each advertising back represents a different type, or maybe these are sub-types. Same for T205, T206, etc– if you just want to see what the card looks like from the front, acquiring one example of a T206 would satisfy your objective to have a card of that “type”, and then you move on to something else that is different. Many would instead want a T206 with each “type” of advertising back and factory designation, but again, generally only one example of each.
I’m sure you get the idea, and see that it can take you in different directions. Player collectors are a more specialized example of type collecting, and some consider back variations to be their own types, such as different fonts, word spacing or orientation– even stock (e.g. gray or white back Topps cards from the 50's). As a concept it is basically the opposite of set collecting–one from all as opposed to all from one. For this reason true type collectors try and snag a card from an issue that is seldom seen, especially since there is little temptation to try and chase a set that may be impossible or is unknown to exist in complete form. In any event and like most here would say, collect what you like!
Here are a couple of mine:
