A "lidded jar" is a container with a cover that fits tightly over the top. It is like a box with a lid, but usually made out of glass or ceramics. Full definition
The overnight oatmeal can be stored for 3 - 4 days with a tight lid jar. (livingvazzy.com)
However, you can simply use a bowl if you're preparing your breakfast one day ahead (you can store them for around 4 days with a tight lid jar). (livingvazzy.com)
Leftovers are best gobbled up within 24 hours — otherwise you might get some avo flavour starting to peek through; store in lidded jar in your refrigerator (jam jars are perfect ♥). (thekitchenrebellion.com)