The phrase "gap fillers" refers to things or people that are used to fill or bridge a space or a lack of something. They come in handy when something is missing or incomplete, and they help make things whole or complete again. Full definition
These small pearl white mercury glass ornaments are perfect little gap fillers when filling vessels with ornaments to decorate the home. (christmastablescapedecor.com)
We don't need any more gap fillers like we've been signing recently, all the gaps have now been filled (well, other than 1 more DM). (justarsenal.com)
Wenger activiting Vardy's release clause, just goes to show that he isn't looking to sign a top top strike, So wheres the logic in looking at WC striker's now, when Wenger's first choice was a mere gap filler for Welbeck? (justarsenal.com)