Naivedyam is a Sanskrit word which means the supplication food offered to the God of worship as a part of ritualistic worship. It is also called nipunson or naivedhya. Naivedyam as a rule is offered to God first before it is accepted (eaten) by the devotees. Tasting Naivedyam during its preparation or eating it before offering it to God is restricted.
To offer Naivedyam, the food is placed before the deity. The devotees recite the mantra seeking divine acceptance for the offering made. However, if you do not know the mantras invoking the divinity for accepting food, you can say a prayer from heart (with devotion) asking God to accept the food and seek his blessings therewith. Once the offering is complete the Naivedyam becomes Prasadam- which is food brought/ distributed to the devotees for consuming. Thus Naivedyam is what is offered to God and Prasad (Prasadam) is what one gets from the God.
Naivedyam includes cooked food (vegetarian without onions and garlic), sugarcane, dry and fresh fruits.