The word "casa" translates to "house" or "home" in English. The word is found in Spanish, Portuguese, Italian and Romanian, and means the same in all four tongues.
The reason that Spanish, Portuguese, Italian and Romanian share this word is that all four languages are Romance languages; that is to say, languages that have evolved from Latin.
The Latin word "casa" meant "cottage", "hut" or "house," and this meaning has carried over into the modern languages. There are several smaller languages that are also related to Latin, and some of these also use the word "casa," such as Catalan, Aragonese and Asturian.