What do you mean by ground state ?

What do you mean by petroleum?

What do you mean by combustion?

What do you mean by constant acceleration ?

What do you mean by representative elements? Name the groups of the periodic table, which contain representative elements.

What do you mean by an ecosystem?

What do you mean by hunger pangs ?

What do you mean by "rancidity"?

What do you mean by staple food?

What do you mean by presbyopia ? How is it corrected ?