The home construction and design industry makes a distinction between the terms "porch" and "patio." As construction styles vary widely, there will be overlap in the definitions, but in general, a porch is part of the home's structure and serves as an entryway to the home. A patio is a paved or hard-scaped surface not part of the structure but often next to it.
If it's built onto the structure itself, it's likely a porch. Porches typically are covered and can be enclosed as with a screen porch or a three-season porch. A porch may be at the front, back or side of a house. Wherever it is, it must provide access to the home's interior; as the National Association of Certified Home Inspectors notes, the word "porch" derives from the Latin "porta," for entrance or gate.
Patios are flat, ground-level surfaces used for outdoor activity. They're usually paved with concrete, brick or other masonry, although a patio can be made of loose gravel or some other hard-scaping material. Patios may be covered, as with a pergola or awning, and some patios are built underneath decks. They're not typically enclosed, though; the word patio derives, by way of Spanish, from the Latin "patere," which refers to something that's open. For convenience sake, patios may be located adjacent to a home and at an entrance.