A porch was an area directly in front of a building's exit where one could sit.
After asking permission to build a nursery for Eline while reliving Kamin's existence in 2368, Jean-Luc Picard gave her the option of a porch instead, saying it would be easier to build. She chose the former. (TNG: "The Inner Light")
The house on the farmyard created by the Caretaker aboard his array had a porch from where Aunt Adah gave out her sugar cookies and lemonade. (VOY: "Caretaker")
In 2372, Quinn recalled sitting on the porch prior to his confinement. (VOY: "Death Wish")