literally umbrella generally means 伞, i think 雨伞 is used to distinguish from 太阳伞/阳伞, which is used for blocking sunshine...( mostly used in china )

in China，雨伞=伞=阳伞=遮阳伞=太阳伞。不同的说法而已。

um.brel.la Qm`brZlE;Qm5brelE <<名詞>> 1 雨傘 2 a. 覆蓋的東西; 具有保護性的東西 b. (軍事行動的) 空中掩護 3 總括 4『動物』水母的傘 <<形容詞>> um.brella.less