Complex sentence: Soft references behave almost identically to weak references, but they are garbage-collected less aggressively: the garbage collector will always collect weakly referenced objects, but will only collect softly referenced objects when its algorithms decide that memory is low enough to warrant it.
Split into simpler sentences: Soft references behave almost identically to weak references, but they are garbage-collected less aggressively. Soft and weak references provide two quasi-priorities for non-strongly referenced objects: the garbage collector will always collect weakly referenced objects, but will only collect softly referenced objects when its algorithms decide that memory is low enough to warrant it.