When faced with five subtly different things, would you rather see one page with a general description of all five, or five pages precisely describing one entry each? If the first, you're a Lumper. If the second, you're a Splitter.
For example: A Splitter is someone who thinks that this page should not exist. There should be separate pages for "Lumper" and "Splitter".
A lumper also wants to get rid of this page, but by merging it with a bunch of other pages to create a new page called "Common Wiki Wars".
The way Tropers handle this deep philosophical divide is for splitters to write finely-distinct entries and for lumpers to write overview entries that list the "splits". We call those lumper pieces "indexes" or Super Tropes, and each of the splits is a Sub-Trope.