Keyword Combinations are the multi-word searches an App Store listing can appear for by combining words from its app name, subtitle and keyword field — so each word needs to appear only once.
On the App Store, the searchable words in an app's name, subtitle and keyword field work as one pool rather than three separate lists. Apple doesn't document the matching logic in detail, but its guidance is consistent with it: developers are told not to repeat any word already in the app name, subtitle or category, and plurals such as "climb" and "climbs" count as duplicates. In practice, ASO teams routinely see a listing with "budget" in the subtitle and "planner" in the keyword field surface for "budget planner" without the phrase appearing anywhere verbatim. Google Play has no keyword field; its matching draws on the visible title and descriptions.
Combinations are what let a 100-character field reach far more phrases than it could spell out. Supplying single words separated by commas, rather than full phrases, lets a short list cover many long-tail searches, and every repeat removed frees room for a new term. Practitioners observe that combinations aren't equal: phrases whose words sit together in the app name tend to rank more strongly than ones assembled across fields, so the single most valuable phrase belongs intact in the name or subtitle. Listing every ordering of a few core words, as the Keyword Shuffler does, shows which phrases a set of words can reach.
Example
A hiking app with "Hiking Maps" in its name adds "offline,gps,trails,elevation,backpacking" to its keyword field. Without repeating "hiking" or "maps", it becomes eligible for phrases like "offline hiking maps" and "gps trails", and the characters it saved go to new words instead of duplicates.