(a) The trait which can express its effect over contrasting trait is called dominant trait whereas the trait which cannot express its effect over contrasting trait or which gets suppressed by the contrasting trait is called recessive trait. The inherited trait which is not expressed will be a recessive trait.
(b) Yes; in Mendel's experiment, when pure tall pea plants were crossed with pure dwarf pea plants, only tall pea plants were obtained in F1 generation. On selfing the pea plants of F1 generation both tall and dwarf pea plants were obtained in F2 generation. Reappearance of the dwarf pea plants in F2 generation proves that the dwarf trait was inherited but not expressed in F1 generation. The recessive trait does not express itself in the presence of the dominant trait. So, it is possible that one trait may be inherited but may not be expressed in an organism.