The pyspark.sql.functions.broadcast function is used to hint that a DataFrame is small enough to be broadcasted during a join operation. This means the DataFrame will be stored in memory on all executors, which is beneficial for avoiding the shuffling of large DataFrames across the network. Option D accurately describes this functionality. The other options are incorrect because they either misinterpret the function's purpose by referring to columns instead of DataFrames (A and B) or describe unrelated caching mechanisms (C and E), which are not temporary and specific to the join operation like broadcast joins are.