Terrasse vs. patio
The French words terrasse and patio both refer to paved outdoor sitting areas, but they describe very different architectural layouts. A terrasse is generally an open outdoor space attached to the exterior of a building, such as a deck or the sidewalk seating of a café. In contrast, a patio is an enclosed or semi-enclosed inner courtyard surrounded by the walls of a house.
Terrasse
A terrasse is an outdoor paved or wooden platform attached to a building, open to the surrounding environment, and is famously used to describe the outdoor seating area of a restaurant or café.
Nous allons manger sur la terrasse ce soir.
(We are going to eat on the terrace tonight.)
Les serveurs nettoient les tables de la terrasse.
(The waiters are cleaning the tables of the terrace.)
Elle adore boire son café en terrasse le matin.
(She loves drinking her coffee on the terrace in the morning.)
Leur nouvelle maison possède une grande terrasse en bois.
(Their new house has a large wooden deck.)
De la terrasse, on a une vue magnifique sur la mer.
(From the terrace, we have a magnificent view of the sea.)
Il fait beaucoup trop froid pour dîner sur la terrasse.
(It is way too cold to have dinner on the terrace.)
Patio
A patio is an internal courtyard or a paved outdoor area that is enclosed or heavily sheltered by the walls of a building, offering a private space in the middle of a home.
L'architecte a dessiné une grande maison avec un patio central.
(The architect designed a large house with a central patio.)
Ils ont installé une petite fontaine au milieu du patio.
(They installed a small fountain in the middle of the patio.)
Le patio est rempli de belles plantes tropicales.
(The inner courtyard is filled with beautiful tropical plants.)
Ce vieux riad marocain possède un patio ombragé.
(This old Moroccan riad has a shaded patio.)
La lumière naturelle entre dans le salon grâce au patio.
(Natural light enters the living room thanks to the patio.)
Nous avons pris le petit-déjeuner dans le patio à l'abri du vent.
(We had breakfast in the courtyard sheltered from the wind.)
Summary
In summary, use terrasse when talking about open outdoor extensions of a house or café seating that look outward. Choose patio when describing a sheltered, enclosed inner courtyard surrounded by the walls of a building that creates an inward-facing private space.