Compatibility is the ability of two or more mods to work together. There are a number of factors that influence mod compatibility, and can create problems when certain mods are used together. Problems stemming from compatibility issues include crashing, dramatic performance loss, dysfunctional features, and other unexpected or unintended game behavior. Compatibility notes are the solution Mod Picker offers for tracking compatibility issues between mods.
Asset conflicts occur when two or more mods change the same asset file. Mod lists on Mod Picker list all assets that conflict in this way. You can also use Mod Organizer to evaluate conflicting assets between mods in your mod list.
Most asset conflicts do not require compatibility patches and can be managed through altering mod installation order.
Record conflicts occur when two or more mods change fields on the same plugin record. This type of conflict only applies to games that have a plugin system such as Skyrim and Fallout 4. Mod lists on Mod Picker list all records that conflict in this way, though do not specify what record fields the conflicts are on.
It's recommend to use xEdit (aka TES5Edit, FO4Edit, etc.) to evaluate record conflicts. xEdit allows you to filter for conflicting records, view different versions of a record side-by-side, and hide non-conflicting fields.
Utilities such as Wrye Bash and Mator Smash can be used to generate a conflict resolution patch for the plugins in your load order. You can also build patches by hand fairly easily using xEdit.
Script conflicts occur when two or more scripts conflict with each other. These conflicts can be hard to detect and resolve. These conflicts are usually found when using mods together in a game. Papyrus logs are helpful for locating the source of script conflicts in Bethesda Games.
Abstract conflicts are issues which don't involve asset or record conflicts, but rather a conflict in scope. Mods which modify the same component of the game in very different ways can be said to have divergent scopes and often shouldn't be used together because the are inconsistent with each other.
Abstract conflicts aren't very easy to detect, and can be a matter of personal preference at times. They can sometimes be patched, though in many cases it may not make sense to do so.
Many compatibility issues can be resolved with compatibility patches. Compatibility patches often simply resolve record conflicts between plugins, but sometimes require more in-depth approaches to resolve asset, script, or abstract conflicts. Most mod authors offer compatibility patches for their mods and popular mods they conflict with.