Your skin is a combination skin if it is dry or normal in some areas and oily in others, such as the famous T-zone (chin, nose and forehead). Combination skin is very demanding as different zones need different treatment!
Oily skin is a skin which produces too much sebum. People with oily skin typically complain on enlarged pores, shiny complexion, blackheads, pimples and other imperfections. Oily skin is more prone to acne as sebum can quickly clogg pores... but don't worry - nature has some great ingredients to take care of oily and combination skin types!