A weak solution is a mixture in which one or more solutes are present in such small amounts that they do not significantly affect the properties of the solvent. Full definition
It is often recommended to use a very, very weak solution of bleach to wash litter trays. (best-cat-art.com)
On Earth, atmospheric CO2 is absorbed by precipitation --- by rain — and forms a very weak solution of carbonic acid, a very mild form of acid rain. (phys.lsu.edu)
We found the map left in the stronger tea solution was noticeably darker than the weaker solution, which is what we expected. (science-sparks.com)