The Mandarin Chinese phrase '假如 (jiǎrú)' is used when talking about theoretical or hypothetical situations. It is equivalent to the English word 'if', and is used to set up a condition that could potentially happen, although it may not be certain or actual. The phrase '假如' is followed by a clause that depicts the hypothetical scenario. Remember, '假如' refers to situations that are less definite or less factual.