A chemical is said to be soluble if it can dissolve into a type of liquid. For example, salt is water soluble. If we were to put salt into water, it would dissolve, and we'd get salt water! Different chemicals will be soluble in different types of liquids.

For example, grease is not water soluble - the grease left in a pan after you cook won't dissolve into water. This can make it tricky to clean. Soap is something that sticks to grease and makes it soluble into water, which makes it easier to clean.