If a colour or dirty mark washes out, or if you wash it out, it disappears when you wash it.

Do you think these stains will wash out? 你说这些污迹洗得掉吗？

If an event or sports competition is washed out, it is prevented from happening or stopped early because of heavy rain.

The men's tennis semifinals were washed out this morning. 今天上午的男子网球半决赛因雨被迫取消。

See also: washout (CANCELLED EVENT)