Stock solution can be defined as a highly concentrated solution, mostly prepared as 10X concentrated, which can be diluted to prepare working solution.
Stock solution is also used as a component to prepare complex solution containing many ingredients. For example, stock solution of EDTA (0.5 M EDTA solution) can be used to prepare many solutions including TAE, TBE, Tris-EDTA, Trypsin-EDTA etc.
Since stock solution is highly concentrated, its storage requires less space.
It is also convenient to transport stock solution due to its small volume.
The concentration of various component of working solution is more accurate when it is made from stock solution rather than individual component from its original form.
Stock solutions which contains any active biological substances (e.g., enzymes, inhibitors, DNA, RNA etc.) are more stable in highly concentrated form.
Since stock solution is highly concentrated, often to dissolve them requires more time and effort. Sometime, heating of solution is required to dissolve the substance completely.
Long term storage of stock solution (especially salt solution, at cold room) may leads to precipitation of solute.