an assessee is a person who pays tax....all the persons do not pay tax....here person also includes companies,partnership firms,huf,aop,boi,co operative societies etc....so all persons are not assessees because everyone does not pay income tax whereas all assessee's are person because only a person paying tax can be called assessee. now u are clear i think...
For example individuals having total income below BEL are not liable to pay tax...and hence not treated as assessee but they are persons as person includes interalia individuals...