'Robes' in the Bible

After these things I looked, and behold, a great multitude, which no man could number, out of every nation and of all tribes, peoples, and languages, standing before the throne and before the Lamb, dressed in white robes, with palm branches in their hands.

One of the elders answered, saying to me, "These who are arrayed in white robes, who are they, and from where did they come?"

I told him, "My lord, you know." He said to me, "These are those who came out of the great tribulation. They washed their robes, and made them white in the Lamb's blood.