In general, there are three types of runs. The first type is the any% run,
where you do whatever it takes to get to the end of the game as fast as possible, acquiring or ignoring items as you see fit. This can be considered the "default" category.
Next is the low%, where you get the bare minimum number of items and upgrades necessary to complete the game, and still try to go as quickly as possible. This can be subjective, so ask Flip or discuss on the forum if you are unsure what constitutes a low% for your game. A low% run does not restrict the usage of items you are forced to obtain. A good example is in Mega Man games, where you always collect a weapon from each robot master or Maverick. You shouldn't minimize the use of your weapons or your run will be rejected.
The low% run will almost always be slower than the any% run, but sometimes skipping everything possible might be the fastest method. In this case, the two categories are functionally the same, and the run will be listed as low% since that is more restrictive.
The third type of run is the 100% run where you collect "everything" in the game.
How to define 100% for any given game is usually quite subjective unless the game tracks percentage, and some games just don't lend themselves to a 100% category. Because of this, it is imperative to ask Flip or discuss the 100% definition on the forum. Generally, we prefer concise, non-arbitrary definitions (instead of "comprehensive" laundry lists) that allow enough differentiation from the any%. A good example is "all stages." A bad example is "all items" in an RPG. Do you need max of each? What about dummy items? Mutually exclusive items? If we're getting all items, why not all skills? Max levels? Max playtime? And so on.