"Observable universe" does indeed refer to the bit of the universe that we can observe. Since the universe is approximately 15 billion years old (plus or minus a few billion years depending on who you are asking) the observable universe is around 15 billion light years in radius.. That amounts to around 142,000,000,000,000,000,000,000 km or 88,000,000,000,000,000,000,000 miles. More numbers that are too large to mean anything to us
